API Access Control

• 1: Authenticating
• 2: Authenticating with Bootstrap Tokens
• 3: Authorization
• 4: Using RBAC Authorization
• 5: Using Node Authorization
• 6: Webhook Mode
• 7: Using ABAC Authorization
• 8: Admission Control in Kubernetes
• 9: Dynamic Admission Control
• 10: Managing Service Accounts
• 11: Certificates and Certificate Signing Requests
• 12: Mapping PodSecurityPolicies to Pod Security Standards
• 13: Kubelet authentication/authorization
• 14: TLS bootstrapping
• 15: Mutating Admission Policy
• 16: Validating Admission Policy

1 - Authenticating

This page provides an overview of authentication.

Users in Kubernetes

All Kubernetes clusters have two categories of users: service accounts managed by Kubernetes, and normal users.

It is assumed that a cluster-independent service manages normal users in the following ways:

• an administrator distributing private keys
• a user store like Keystone or Google Accounts
• a file with a list of usernames and passwords

In this regard, Kubernetes does not have objects which represent normal user accounts. Normal users cannot be added to a cluster through an API call.

Even though a normal user cannot be added via an API call, any user that presents a valid certificate signed by the cluster's certificate authority (CA) is considered authenticated. In this configuration, Kubernetes determines the username from the common name field in the 'subject' of the cert (e.g., "/CN=bob"). From there, the role based access control (RBAC) sub-system would determine whether the user is authorized to perform a specific operation on a resource. For more details, refer to the normal users topic in certificate request for more details about this.

In contrast, service accounts are users managed by the Kubernetes API. They are bound to specific namespaces, and created automatically by the API server or manually through API calls. Service accounts are tied to a set of credentials stored as Secrets, which are mounted into pods allowing in-cluster processes to talk to the Kubernetes API.

API requests are tied to either a normal user or a service account, or are treated as anonymous requests. This means every process inside or outside the cluster, from a human user typing kubectl on a workstation, to kubelets on nodes, to members of the control plane, must authenticate when making requests to the API server, or be treated as an anonymous user.

Authentication strategies

Kubernetes uses client certificates, bearer tokens, or an authenticating proxy to authenticate API requests through authentication plugins. As HTTP requests are made to the API server, plugins attempt to associate the following attributes with the request:

• Username: a string which identifies the end user. Common values might be kube-admin or jane@example.com.
• UID: a string which identifies the end user and attempts to be more consistent and unique than username.
• Groups: a set of strings, each of which indicates the user's membership in a named logical collection of users. Common values might be system:masters or devops-team.
• Extra fields: a map of strings to list of strings which holds additional information authorizers may find useful.

All values are opaque to the authentication system and only hold significance when interpreted by an authorizer.

You can enable multiple authentication methods at once. You should usually use at least two methods:

• service account tokens for service accounts
• at least one other method for user authentication.

When multiple authenticator modules are enabled, the first module to successfully authenticate the request short-circuits evaluation. The API server does not guarantee the order authenticators run in.

The system:authenticated group is included in the list of groups for all authenticated users.

Integrations with other authentication protocols (LDAP, SAML, Kerberos, alternate x509 schemes, etc) can be accomplished using an authenticating proxy or the authentication webhook.

X509 client certificates

Client certificate authentication is enabled by passing the --client-ca-file=SOMEFILE option to API server. The referenced file must contain one or more certificate authorities to use to validate client certificates presented to the API server. If a client certificate is presented and verified, the common name of the subject is used as the user name for the request. As of Kubernetes 1.4, client certificates can also indicate a user's group memberships using the certificate's organization fields. To include multiple group memberships for a user, include multiple organization fields in the certificate.

For example, using the openssl command line tool to generate a certificate signing request:

openssl req -new -key jbeda.pem -out jbeda-csr.pem -subj "/CN=jbeda/O=app1/O=app2"

This would create a CSR for the username "jbeda", belonging to two groups, "app1" and "app2".

See Managing Certificates for how to generate a client cert.

Static token file

The API server reads bearer tokens from a file when given the --token-auth-file=SOMEFILE option on the command line. Currently, tokens last indefinitely, and the token list cannot be changed without restarting the API server.

The token file is a csv file with a minimum of 3 columns: token, user name, user uid, followed by optional group names.

token,user,uid,"group1,group2,group3"

Putting a bearer token in a request

When using bearer token authentication from an http client, the API server expects an Authorization header with a value of Bearer <token>. The bearer token must be a character sequence that can be put in an HTTP header value using no more than the encoding and quoting facilities of HTTP. For example: if the bearer token is 31ada4fd-adec-460c-809a-9e56ceb75269 then it would appear in an HTTP header as shown below.

Authorization: Bearer 31ada4fd-adec-460c-809a-9e56ceb75269

Bootstrap tokens

To allow for streamlined bootstrapping for new clusters, Kubernetes includes a dynamically-managed Bearer token type called a Bootstrap Token. These tokens are stored as Secrets in the kube-system namespace, where they can be dynamically managed and created. Controller Manager contains a TokenCleaner controller that deletes bootstrap tokens as they expire.

The tokens are of the form [a-z0-9]{6}.[a-z0-9]{16}. The first component is a Token ID and the second component is the Token Secret. You specify the token in an HTTP header as follows:

Authorization: Bearer 781292.db7bc3a58fc5f07e

You must enable the Bootstrap Token Authenticator with the --enable-bootstrap-token-auth flag on the API Server. You must enable the TokenCleaner controller via the --controllers flag on the Controller Manager. This is done with something like --controllers=*,tokencleaner. kubeadm will do this for you if you are using it to bootstrap a cluster.

The authenticator authenticates as system:bootstrap:<Token ID>. It is included in the system:bootstrappers group. The naming and groups are intentionally limited to discourage users from using these tokens past bootstrapping. The user names and group can be used (and are used by kubeadm) to craft the appropriate authorization policies to support bootstrapping a cluster.

Please see Bootstrap Tokens for in depth documentation on the Bootstrap Token authenticator and controllers along with how to manage these tokens with kubeadm.

Service account tokens

A service account is an automatically enabled authenticator that uses signed bearer tokens to verify requests. The plugin takes two optional flags:

• --service-account-key-file File containing PEM-encoded x509 RSA or ECDSA private or public keys, used to verify ServiceAccount tokens. The specified file can contain multiple keys, and the flag can be specified multiple times with different files. If unspecified, --tls-private-key-file is used.
• --service-account-lookup If enabled, tokens which are deleted from the API will be revoked.

Service accounts are usually created automatically by the API server and associated with pods running in the cluster through the ServiceAccount Admission Controller. Bearer tokens are mounted into pods at well-known locations, and allow in-cluster processes to talk to the API server. Accounts may be explicitly associated with pods using the serviceAccountName field of a PodSpec.

apiVersion: apps/v1 # this apiVersion is relevant as of Kubernetes 1.9
kind: Deployment
metadata:
  name: nginx-deployment
  namespace: default
spec:
  replicas: 3
  template:
    metadata:
    # ...
    spec:
      serviceAccountName: bob-the-bot
      containers:
      - name: nginx
        image: nginx:1.14.2

Service account bearer tokens are perfectly valid to use outside the cluster and can be used to create identities for long standing jobs that wish to talk to the Kubernetes API. To manually create a service account, use the kubectl create serviceaccount (NAME) command. This creates a service account in the current namespace.

kubectl create serviceaccount jenkins

serviceaccount/jenkins created

Create an associated token:

kubectl create token jenkins

eyJhbGciOiJSUzI1NiIsImtp...

The created token is a signed JSON Web Token (JWT).

The signed JWT can be used as a bearer token to authenticate as the given service account. See above for how the token is included in a request. Normally these tokens are mounted into pods for in-cluster access to the API server, but can be used from outside the cluster as well.

Service accounts authenticate with the username system:serviceaccount:(NAMESPACE):(SERVICEACCOUNT), and are assigned to the groups system:serviceaccounts and system:serviceaccounts:(NAMESPACE).

OpenID Connect Tokens

OpenID Connect is a flavor of OAuth2 supported by some OAuth2 providers, notably Microsoft Entra ID, Salesforce, and Google. The protocol's main extension of OAuth2 is an additional field returned with the access token called an ID Token. This token is a JSON Web Token (JWT) with well known fields, such as a user's email, signed by the server.

To identify the user, the authenticator uses the id_token (not the access_token) from the OAuth2 token response as a bearer token. See above for how the token is included in a request.

1. Log in to your identity provider

2. Your identity provider will provide you with an access_token, id_token and a refresh_token

3. When using kubectl, use your id_token with the --token flag or add it directly to your kubeconfig

4. kubectl sends your id_token in a header called Authorization to the API server

5. The API server will make sure the JWT signature is valid

6. Check to make sure the id_token hasn't expired

   Perform claim and/or user validation if CEL expressions are configured with AuthenticationConfiguration.

7. Make sure the user is authorized

8. Once authorized the API server returns a response to kubectl

9. kubectl provides feedback to the user

Since all of the data needed to validate who you are is in the id_token, Kubernetes doesn't need to "phone home" to the identity provider. In a model where every request is stateless this provides a very scalable solution for authentication. It does offer a few challenges:

1. Kubernetes has no "web interface" to trigger the authentication process. There is no browser or interface to collect credentials which is why you need to authenticate to your identity provider first.
2. The id_token can't be revoked, it's like a certificate so it should be short-lived (only a few minutes) so it can be very annoying to have to get a new token every few minutes.
3. To authenticate to the Kubernetes dashboard, you must use the kubectl proxy command or a reverse proxy that injects the id_token.

Configuring the API Server

Using flags

To enable the plugin, configure the following flags on the API server:

Authentication configuration from a file

JWT Authenticator is an authenticator to authenticate Kubernetes users using JWT compliant tokens. The authenticator will attempt to parse a raw ID token, verify it's been signed by the configured issuer. The public key to verify the signature is discovered from the issuer's public endpoint using OIDC discovery.

The minimum valid JWT payload must contain the following claims:

{
  "iss": "https://example.com",   // must match the issuer.url
  "aud": ["my-app"],              // at least one of the entries in issuer.audiences must match the "aud" claim in presented JWTs.
  "exp": 1234567890,              // token expiration as Unix time (the number of seconds elapsed since January 1, 1970 UTC)
  "<username-claim>": "user"      // this is the username claim configured in the claimMappings.username.claim or claimMappings.username.expression
}

The configuration file approach allows you to configure multiple JWT authenticators, each with a unique issuer.url and issuer.discoveryURL. The configuration file even allows you to specify CEL expressions to map claims to user attributes, and to validate claims and user information. The API server also automatically reloads the authenticators when the configuration file is modified. You can use apiserver_authentication_config_controller_automatic_reload_last_timestamp_seconds metric to monitor the last time the configuration was reloaded by the API server.

You must specify the path to the authentication configuration using the --authentication-config flag on the API server. If you want to use command line flags instead of the configuration file, those will continue to work as-is. To access the new capabilities like configuring multiple authenticators, setting multiple audiences for an issuer, switch to using the configuration file.

For Kubernetes v1.32, the structured authentication configuration file format is beta-level, and the mechanism for using that configuration is also beta. Provided you didn't specifically disable the StructuredAuthenticationConfiguration feature gate for your cluster, you can turn on structured authentication by specifying the --authentication-config command line argument to the kube-apiserver. An example of the structured authentication configuration file is shown below.

---
#
# CAUTION: this is an example configuration.
#          Do not use this for your own cluster!
#
apiVersion: apiserver.config.k8s.io/v1beta1
kind: AuthenticationConfiguration
# list of authenticators to authenticate Kubernetes users using JWT compliant tokens.
# the maximum number of allowed authenticators is 64.
jwt:
- issuer:
    # url must be unique across all authenticators.
    # url must not conflict with issuer configured in --service-account-issuer.
    url: https://example.com # Same as --oidc-issuer-url.
    # discoveryURL, if specified, overrides the URL used to fetch discovery
    # information instead of using "{url}/.well-known/openid-configuration".
    # The exact value specified is used, so "/.well-known/openid-configuration"
    # must be included in discoveryURL if needed.
    #
    # The "issuer" field in the fetched discovery information must match the "issuer.url" field
    # in the AuthenticationConfiguration and will be used to validate the "iss" claim in the presented JWT.
    # This is for scenarios where the well-known and jwks endpoints are hosted at a different
    # location than the issuer (such as locally in the cluster).
    # discoveryURL must be different from url if specified and must be unique across all authenticators.
    discoveryURL: https://discovery.example.com/.well-known/openid-configuration
    # PEM encoded CA certificates used to validate the connection when fetching
    # discovery information. If not set, the system verifier will be used.
    # Same value as the content of the file referenced by the --oidc-ca-file flag.
    certificateAuthority: <PEM encoded CA certificates>    
    # audiences is the set of acceptable audiences the JWT must be issued to.
    # At least one of the entries must match the "aud" claim in presented JWTs.
    audiences:
    - my-app # Same as --oidc-client-id.
    - my-other-app
    # this is required to be set to "MatchAny" when multiple audiences are specified.
    audienceMatchPolicy: MatchAny
  # rules applied to validate token claims to authenticate users.
  claimValidationRules:
    # Same as --oidc-required-claim key=value.
  - claim: hd
    requiredValue: example.com
    # Instead of claim and requiredValue, you can use expression to validate the claim.
    # expression is a CEL expression that evaluates to a boolean.
    # all the expressions must evaluate to true for validation to succeed.
  - expression: 'claims.hd == "example.com"'
    # Message customizes the error message seen in the API server logs when the validation fails.
    message: the hd claim must be set to example.com
  - expression: 'claims.exp - claims.nbf <= 86400'
    message: total token lifetime must not exceed 24 hours
  claimMappings:
    # username represents an option for the username attribute.
    # This is the only required attribute.
    username:
      # Same as --oidc-username-claim. Mutually exclusive with username.expression.
      claim: "sub"
      # Same as --oidc-username-prefix. Mutually exclusive with username.expression.
      # if username.claim is set, username.prefix is required.
      # Explicitly set it to "" if no prefix is desired.
      prefix: ""
      # Mutually exclusive with username.claim and username.prefix.
      # expression is a CEL expression that evaluates to a string.
      #
      # 1.  If username.expression uses 'claims.email', then 'claims.email_verified' must be used in
      #     username.expression or extra[*].valueExpression or claimValidationRules[*].expression.
      #     An example claim validation rule expression that matches the validation automatically
      #     applied when username.claim is set to 'email' is 'claims.?email_verified.orValue(true)'.
      # 2.  If the username asserted based on username.expression is the empty string, the authentication
      #     request will fail.
      expression: 'claims.username + ":external-user"'
    # groups represents an option for the groups attribute.
    groups:
      # Same as --oidc-groups-claim. Mutually exclusive with groups.expression.
      claim: "sub"
      # Same as --oidc-groups-prefix. Mutually exclusive with groups.expression.
      # if groups.claim is set, groups.prefix is required.
      # Explicitly set it to "" if no prefix is desired.
      prefix: ""
      # Mutually exclusive with groups.claim and groups.prefix.
      # expression is a CEL expression that evaluates to a string or a list of strings.
      expression: 'claims.roles.split(",")'
    # uid represents an option for the uid attribute.
    uid:
      # Mutually exclusive with uid.expression.
      claim: 'sub'
      # Mutually exclusive with uid.claim
      # expression is a CEL expression that evaluates to a string.
      expression: 'claims.sub'
    # extra attributes to be added to the UserInfo object. Keys must be domain-prefix path and must be unique.
    extra:
      # key is a string to use as the extra attribute key.
      # key must be a domain-prefix path (e.g. example.org/foo). All characters before the first "/" must be a valid
      # subdomain as defined by RFC 1123. All characters trailing the first "/" must
      # be valid HTTP Path characters as defined by RFC 3986.
      # k8s.io, kubernetes.io and their subdomains are reserved for Kubernetes use and cannot be used.
      # key must be lowercase and unique across all extra attributes.
    - key: 'example.com/tenant'
      # valueExpression is a CEL expression that evaluates to a string or a list of strings.
      valueExpression: 'claims.tenant'
  # validation rules applied to the final user object.
  userValidationRules:
    # expression is a CEL expression that evaluates to a boolean.
    # all the expressions must evaluate to true for the user to be valid.
  - expression: "!user.username.startsWith('system:')"
    # Message customizes the error message seen in the API server logs when the validation fails.
    message: 'username cannot used reserved system: prefix'
  - expression: "user.groups.all(group, !group.startsWith('system:'))"
    message: 'groups cannot used reserved system: prefix'

• Claim validation rule expression

  jwt.claimValidationRules[i].expression represents the expression which will be evaluated by CEL. CEL expressions have access to the contents of the token payload, organized into claims CEL variable. claims is a map of claim names (as strings) to claim values (of any type).

• User validation rule expression

  jwt.userValidationRules[i].expression represents the expression which will be evaluated by CEL. CEL expressions have access to the contents of userInfo, organized into user CEL variable. Refer to the UserInfo API documentation for the schema of user.

• Claim mapping expression

  jwt.claimMappings.username.expression, jwt.claimMappings.groups.expression, jwt.claimMappings.uid.expression jwt.claimMappings.extra[i].valueExpression represents the expression which will be evaluated by CEL. CEL expressions have access to the contents of the token payload, organized into claims CEL variable. claims is a map of claim names (as strings) to claim values (of any type).

  To learn more, see the Documentation on CEL

  Here are examples of the AuthenticationConfiguration with different token payloads.

  • Valid token
  • Fails claim validation
  • Fails user validation

  apiVersion: apiserver.config.k8s.io/v1beta1
  kind: AuthenticationConfiguration
  jwt:
  - issuer:
      url: https://example.com
      audiences:
      - my-app
    claimMappings:
      username:
        expression: 'claims.username + ":external-user"'
      groups:
        expression: 'claims.roles.split(",")'
      uid:
        expression: 'claims.sub'
      extra:
      - key: 'example.com/tenant'
        valueExpression: 'claims.tenant'
    userValidationRules:
    - expression: "!user.username.startsWith('system:')" # the expression will evaluate to true, so validation will succeed.
      message: 'username cannot used reserved system: prefix'
  

  TOKEN=eyJhbGciOiJSUzI1NiIsImtpZCI6ImY3dF9tOEROWmFTQk1oWGw5QXZTWGhBUC04Y0JmZ0JVbFVpTG5oQkgxdXMiLCJ0eXAiOiJKV1QifQ.eyJhdWQiOiJrdWJlcm5ldGVzIiwiZXhwIjoxNzAzMjMyOTQ5LCJpYXQiOjE3MDExMDcyMzMsImlzcyI6Imh0dHBzOi8vZXhhbXBsZS5jb20iLCJqdGkiOiI3YzMzNzk0MjgwN2U3M2NhYTJjMzBjODY4YWMwY2U5MTBiY2UwMmRkY2JmZWJlOGMyM2I4YjVmMjdhZDYyODczIiwibmJmIjoxNzAxMTA3MjMzLCJyb2xlcyI6InVzZXIsYWRtaW4iLCJzdWIiOiJhdXRoIiwidGVuYW50IjoiNzJmOTg4YmYtODZmMS00MWFmLTkxYWItMmQ3Y2QwMTFkYjRhIiwidXNlcm5hbWUiOiJmb28ifQ.TBWF2RkQHm4QQz85AYPcwLxSk-VLvQW-mNDHx7SEOSv9LVwcPYPuPajJpuQn9C_gKq1R94QKSQ5F6UgHMILz8OfmPKmX_00wpwwNVGeevJ79ieX2V-__W56iNR5gJ-i9nn6FYk5pwfVREB0l4HSlpTOmu80gbPWAXY5hLW0ZtcE1JTEEmefORHV2ge8e3jp1xGafNy6LdJWabYuKiw8d7Qga__HxtKB-t0kRMNzLRS7rka_SfQg0dSYektuxhLbiDkqhmRffGlQKXGVzUsuvFw7IGM5ZWnZgEMDzCI357obHeM3tRqpn5WRjtB8oM7JgnCymaJi-P3iCd88iu1xnzA
  

  where the token payload is:

    {
      "aud": "kubernetes",
      "exp": 1703232949,
      "iat": 1701107233,
      "iss": "https://example.com",
      "jti": "7c337942807e73caa2c30c868ac0ce910bce02ddcbfebe8c23b8b5f27ad62873",
      "nbf": 1701107233,
      "roles": "user,admin",
      "sub": "auth",
      "tenant": "72f988bf-86f1-41af-91ab-2d7cd011db4a",
      "username": "foo"
    }
  

  The token with the above AuthenticationConfiguration will produce the following UserInfo object and successfully authenticate the user.

  {
      "username": "foo:external-user",
      "uid": "auth",
      "groups": [
          "user",
          "admin"
      ],
      "extra": {
          "example.com/tenant": "72f988bf-86f1-41af-91ab-2d7cd011db4a"
      }
  }
  

  apiVersion: apiserver.config.k8s.io/v1beta1
  kind: AuthenticationConfiguration
  jwt:
  - issuer:
      url: https://example.com
      audiences:
      - my-app
    claimValidationRules:
    - expression: 'claims.hd == "example.com"' # the token below does not have this claim, so validation will fail.
      message: the hd claim must be set to example.com
    claimMappings:
      username:
        expression: 'claims.username + ":external-user"'
      groups:
        expression: 'claims.roles.split(",")'
      uid:
        expression: 'claims.sub'
      extra:
      - key: 'example.com/tenant'
        valueExpression: 'claims.tenant'
    userValidationRules:
    - expression: "!user.username.startsWith('system:')" # the expression will evaluate to true, so validation will succeed.
      message: 'username cannot used reserved system: prefix'
  

  TOKEN=eyJhbGciOiJSUzI1NiIsImtpZCI6ImY3dF9tOEROWmFTQk1oWGw5QXZTWGhBUC04Y0JmZ0JVbFVpTG5oQkgxdXMiLCJ0eXAiOiJKV1QifQ.eyJhdWQiOiJrdWJlcm5ldGVzIiwiZXhwIjoxNzAzMjMyOTQ5LCJpYXQiOjE3MDExMDcyMzMsImlzcyI6Imh0dHBzOi8vZXhhbXBsZS5jb20iLCJqdGkiOiI3YzMzNzk0MjgwN2U3M2NhYTJjMzBjODY4YWMwY2U5MTBiY2UwMmRkY2JmZWJlOGMyM2I4YjVmMjdhZDYyODczIiwibmJmIjoxNzAxMTA3MjMzLCJyb2xlcyI6InVzZXIsYWRtaW4iLCJzdWIiOiJhdXRoIiwidGVuYW50IjoiNzJmOTg4YmYtODZmMS00MWFmLTkxYWItMmQ3Y2QwMTFkYjRhIiwidXNlcm5hbWUiOiJmb28ifQ.TBWF2RkQHm4QQz85AYPcwLxSk-VLvQW-mNDHx7SEOSv9LVwcPYPuPajJpuQn9C_gKq1R94QKSQ5F6UgHMILz8OfmPKmX_00wpwwNVGeevJ79ieX2V-__W56iNR5gJ-i9nn6FYk5pwfVREB0l4HSlpTOmu80gbPWAXY5hLW0ZtcE1JTEEmefORHV2ge8e3jp1xGafNy6LdJWabYuKiw8d7Qga__HxtKB-t0kRMNzLRS7rka_SfQg0dSYektuxhLbiDkqhmRffGlQKXGVzUsuvFw7IGM5ZWnZgEMDzCI357obHeM3tRqpn5WRjtB8oM7JgnCymaJi-P3iCd88iu1xnzA
  

  where the token payload is:

    {
      "aud": "kubernetes",
      "exp": 1703232949,
      "iat": 1701107233,
      "iss": "https://example.com",
      "jti": "7c337942807e73caa2c30c868ac0ce910bce02ddcbfebe8c23b8b5f27ad62873",
      "nbf": 1701107233,
      "roles": "user,admin",
      "sub": "auth",
      "tenant": "72f988bf-86f1-41af-91ab-2d7cd011db4a",
      "username": "foo"
    }
  

  The token with the above AuthenticationConfiguration will fail to authenticate because the hd claim is not set to example.com. The API server will return 401 Unauthorized error.

  apiVersion: apiserver.config.k8s.io/v1beta1
  kind: AuthenticationConfiguration
  jwt:
  - issuer:
      url: https://example.com
      audiences:
      - my-app
    claimValidationRules:
    - expression: 'claims.hd == "example.com"'
      message: the hd claim must be set to example.com
    claimMappings:
      username:
        expression: '"system:" + claims.username' # this will prefix the username with "system:" and will fail user validation.
      groups:
        expression: 'claims.roles.split(",")'
      uid:
        expression: 'claims.sub'
      extra:
      - key: 'example.com/tenant'
        valueExpression: 'claims.tenant'
    userValidationRules:
    - expression: "!user.username.startsWith('system:')" # the username will be system:foo and expression will evaluate to false, so validation will fail.
      message: 'username cannot used reserved system: prefix'
  

  TOKEN=eyJhbGciOiJSUzI1NiIsImtpZCI6ImY3dF9tOEROWmFTQk1oWGw5QXZTWGhBUC04Y0JmZ0JVbFVpTG5oQkgxdXMiLCJ0eXAiOiJKV1QifQ.eyJhdWQiOiJrdWJlcm5ldGVzIiwiZXhwIjoxNzAzMjMyOTQ5LCJoZCI6ImV4YW1wbGUuY29tIiwiaWF0IjoxNzAxMTEzMTAxLCJpc3MiOiJodHRwczovL2V4YW1wbGUuY29tIiwianRpIjoiYjViMDY1MjM3MmNkMjBlMzQ1YjZmZGZmY2RjMjE4MWY0YWZkNmYyNTlhYWI0YjdlMzU4ODEyMzdkMjkyMjBiYyIsIm5iZiI6MTcwMTExMzEwMSwicm9sZXMiOiJ1c2VyLGFkbWluIiwic3ViIjoiYXV0aCIsInRlbmFudCI6IjcyZjk4OGJmLTg2ZjEtNDFhZi05MWFiLTJkN2NkMDExZGI0YSIsInVzZXJuYW1lIjoiZm9vIn0.FgPJBYLobo9jnbHreooBlvpgEcSPWnKfX6dc0IvdlRB-F0dCcgy91oCJeK_aBk-8zH5AKUXoFTlInfLCkPivMOJqMECA1YTrMUwt_IVqwb116AqihfByUYIIqzMjvUbthtbpIeHQm2fF0HbrUqa_Q0uaYwgy8mD807h7sBcUMjNd215ff_nFIHss-9zegH8GI1d9fiBf-g6zjkR1j987EP748khpQh9IxPjMJbSgG_uH5x80YFuqgEWwq-aYJPQxXX6FatP96a2EAn7wfPpGlPRt0HcBOvq5pCnudgCgfVgiOJiLr_7robQu4T1bis0W75VPEvwWtgFcLnvcQx0JWg
  

  where the token payload is:

    {
      "aud": "kubernetes",
      "exp": 1703232949,
      "hd": "example.com",
      "iat": 1701113101,
      "iss": "https://example.com",
      "jti": "b5b0652372cd20e345b6fdffcdc2181f4afd6f259aab4b7e35881237d29220bc",
      "nbf": 1701113101,
      "roles": "user,admin",
      "sub": "auth",
      "tenant": "72f988bf-86f1-41af-91ab-2d7cd011db4a",
      "username": "foo"
    }
  

  The token with the above AuthenticationConfiguration will produce the following UserInfo object:

  {
      "username": "system:foo",
      "uid": "auth",
      "groups": [
          "user",
          "admin"
      ],
      "extra": {
          "example.com/tenant": "72f988bf-86f1-41af-91ab-2d7cd011db4a"
      }
  }
  

  which will fail user validation because the username starts with system:. The API server will return 401 Unauthorized error.

Limitations

1. Distributed claims do not work via CEL expressions.
2. Egress selector configuration is not supported for calls to issuer.url and issuer.discoveryURL.

Kubernetes does not provide an OpenID Connect Identity Provider. You can use an existing public OpenID Connect Identity Provider (such as Google, or others). Or, you can run your own Identity Provider, such as dex, Keycloak, CloudFoundry UAA, or Tremolo Security's OpenUnison.

For an identity provider to work with Kubernetes it must:

1. Support OpenID connect discovery

   The public key to verify the signature is discovered from the issuer's public endpoint using OIDC discovery. If you're using the authentication configuration file, the identity provider doesn't need to publicly expose the discovery endpoint. You can host the discovery endpoint at a different location than the issuer (such as locally in the cluster) and specify the issuer.discoveryURL in the configuration file.

2. Run in TLS with non-obsolete ciphers

3. Have a CA signed certificate (even if the CA is not a commercial CA or is self signed)

A note about requirement #3 above, requiring a CA signed certificate. If you deploy your own identity provider (as opposed to one of the cloud providers like Google or Microsoft) you MUST have your identity provider's web server certificate signed by a certificate with the CA flag set to TRUE, even if it is self signed. This is due to GoLang's TLS client implementation being very strict to the standards around certificate validation. If you don't have a CA handy, you can use the gencert script from the Dex team to create a simple CA and a signed certificate and key pair. Or you can use this similar script that generates SHA256 certs with a longer life and larger key size.

Refer to setup instructions for specific systems:

• UAA
• Dex
• OpenUnison

Using kubectl

Option 1 - OIDC Authenticator

The first option is to use the kubectl oidc authenticator, which sets the id_token as a bearer token for all requests and refreshes the token once it expires. After you've logged into your provider, use kubectl to add your id_token, refresh_token, client_id, and client_secret to configure the plugin.

Providers that don't return an id_token as part of their refresh token response aren't supported by this plugin and should use "Option 2" below.

kubectl config set-credentials USER_NAME \
   --auth-provider=oidc \
   --auth-provider-arg=idp-issuer-url=( issuer url ) \
   --auth-provider-arg=client-id=( your client id ) \
   --auth-provider-arg=client-secret=( your client secret ) \
   --auth-provider-arg=refresh-token=( your refresh token ) \
   --auth-provider-arg=idp-certificate-authority=( path to your ca certificate ) \
   --auth-provider-arg=id-token=( your id_token )

As an example, running the below command after authenticating to your identity provider:

kubectl config set-credentials mmosley  \
        --auth-provider=oidc  \
        --auth-provider-arg=idp-issuer-url=https://oidcidp.tremolo.lan:8443/auth/idp/OidcIdP  \
        --auth-provider-arg=client-id=kubernetes  \
        --auth-provider-arg=client-secret=1db158f6-177d-4d9c-8a8b-d36869918ec5  \
        --auth-provider-arg=refresh-token=q1bKLFOyUiosTfawzA93TzZIDzH2TNa2SMm0zEiPKTUwME6BkEo6Sql5yUWVBSWpKUGphaWpxSVAfekBOZbBhaEW+VlFUeVRGcluyVF5JT4+haZmPsluFoFu5XkpXk5BXqHega4GAXlF+ma+vmYpFcHe5eZR+slBFpZKtQA= \
        --auth-provider-arg=idp-certificate-authority=/root/ca.pem \
        --auth-provider-arg=id-token=eyJraWQiOiJDTj1vaWRjaWRwLnRyZW1vbG8ubGFuLCBPVT1EZW1vLCBPPVRybWVvbG8gU2VjdXJpdHksIEw9QXJsaW5ndG9uLCBTVD1WaXJnaW5pYSwgQz1VUy1DTj1rdWJlLWNhLTEyMDIxNDc5MjEwMzYwNzMyMTUyIiwiYWxnIjoiUlMyNTYifQ.eyJpc3MiOiJodHRwczovL29pZGNpZHAudHJlbW9sby5sYW46ODQ0My9hdXRoL2lkcC9PaWRjSWRQIiwiYXVkIjoia3ViZXJuZXRlcyIsImV4cCI6MTQ4MzU0OTUxMSwianRpIjoiMm96US15TXdFcHV4WDlHZUhQdy1hZyIsImlhdCI6MTQ4MzU0OTQ1MSwibmJmIjoxNDgzNTQ5MzMxLCJzdWIiOiI0YWViMzdiYS1iNjQ1LTQ4ZmQtYWIzMC0xYTAxZWU0MWUyMTgifQ.w6p4J_6qQ1HzTG9nrEOrubxIMb9K5hzcMPxc9IxPx2K4xO9l-oFiUw93daH3m5pluP6K7eOE6txBuRVfEcpJSwlelsOsW8gb8VJcnzMS9EnZpeA0tW_p-mnkFc3VcfyXuhe5R3G7aa5d8uHv70yJ9Y3-UhjiN9EhpMdfPAoEB9fYKKkJRzF7utTTIPGrSaSU6d2pcpfYKaxIwePzEkT4DfcQthoZdy9ucNvvLoi1DIC-UocFD8HLs8LYKEqSxQvOcvnThbObJ9af71EwmuE21fO5KzMW20KtAeget1gnldOosPtz1G5EwvaQ401-RPQzPGMVBld0_zMCAwZttJ4knw

Which would produce the below configuration:

users:
- name: mmosley
  user:
    auth-provider:
      config:
        client-id: kubernetes
        client-secret: 1db158f6-177d-4d9c-8a8b-d36869918ec5
        id-token: eyJraWQiOiJDTj1vaWRjaWRwLnRyZW1vbG8ubGFuLCBPVT1EZW1vLCBPPVRybWVvbG8gU2VjdXJpdHksIEw9QXJsaW5ndG9uLCBTVD1WaXJnaW5pYSwgQz1VUy1DTj1rdWJlLWNhLTEyMDIxNDc5MjEwMzYwNzMyMTUyIiwiYWxnIjoiUlMyNTYifQ.eyJpc3MiOiJodHRwczovL29pZGNpZHAudHJlbW9sby5sYW46ODQ0My9hdXRoL2lkcC9PaWRjSWRQIiwiYXVkIjoia3ViZXJuZXRlcyIsImV4cCI6MTQ4MzU0OTUxMSwianRpIjoiMm96US15TXdFcHV4WDlHZUhQdy1hZyIsImlhdCI6MTQ4MzU0OTQ1MSwibmJmIjoxNDgzNTQ5MzMxLCJzdWIiOiI0YWViMzdiYS1iNjQ1LTQ4ZmQtYWIzMC0xYTAxZWU0MWUyMTgifQ.w6p4J_6qQ1HzTG9nrEOrubxIMb9K5hzcMPxc9IxPx2K4xO9l-oFiUw93daH3m5pluP6K7eOE6txBuRVfEcpJSwlelsOsW8gb8VJcnzMS9EnZpeA0tW_p-mnkFc3VcfyXuhe5R3G7aa5d8uHv70yJ9Y3-UhjiN9EhpMdfPAoEB9fYKKkJRzF7utTTIPGrSaSU6d2pcpfYKaxIwePzEkT4DfcQthoZdy9ucNvvLoi1DIC-UocFD8HLs8LYKEqSxQvOcvnThbObJ9af71EwmuE21fO5KzMW20KtAeget1gnldOosPtz1G5EwvaQ401-RPQzPGMVBld0_zMCAwZttJ4knw
        idp-certificate-authority: /root/ca.pem
        idp-issuer-url: https://oidcidp.tremolo.lan:8443/auth/idp/OidcIdP
        refresh-token: q1bKLFOyUiosTfawzA93TzZIDzH2TNa2SMm0zEiPKTUwME6BkEo6Sql5yUWVBSWpKUGphaWpxSVAfekBOZbBhaEW+VlFUeVRGcluyVF5JT4+haZmPsluFoFu5XkpXk5BXq
      name: oidc

Once your id_token expires, kubectl will attempt to refresh your id_token using your refresh_token and client_secret storing the new values for the refresh_token and id_token in your .kube/config.

Option 2 - Use the --token Option

The kubectl command lets you pass in a token using the --token option. Copy and paste the id_token into this option:

kubectl --token=eyJhbGciOiJSUzI1NiJ9.eyJpc3MiOiJodHRwczovL21sYi50cmVtb2xvLmxhbjo4MDQzL2F1dGgvaWRwL29pZGMiLCJhdWQiOiJrdWJlcm5ldGVzIiwiZXhwIjoxNDc0NTk2NjY5LCJqdGkiOiI2RDUzNXoxUEpFNjJOR3QxaWVyYm9RIiwiaWF0IjoxNDc0NTk2MzY5LCJuYmYiOjE0NzQ1OTYyNDksInN1YiI6Im13aW5kdSIsInVzZXJfcm9sZSI6WyJ1c2VycyIsIm5ldy1uYW1lc3BhY2Utdmlld2VyIl0sImVtYWlsIjoibXdpbmR1QG5vbW9yZWplZGkuY29tIn0.f2As579n9VNoaKzoF-dOQGmXkFKf1FMyNV0-va_B63jn-_n9LGSCca_6IVMP8pO-Zb4KvRqGyTP0r3HkHxYy5c81AnIh8ijarruczl-TK_yF5akjSTHFZD-0gRzlevBDiH8Q79NAr-ky0P4iIXS8lY9Vnjch5MF74Zx0c3alKJHJUnnpjIACByfF2SCaYzbWFMUNat-K1PaUk5-ujMBG7yYnr95xD-63n8CO8teGUAAEMx6zRjzfhnhbzX-ajwZLGwGUBT4WqjMs70-6a7_8gZmLZb2az1cZynkFRj2BaCkVT3A2RrjeEwZEtGXlMqKJ1_I2ulrOVsYx01_yD35-rw get nodes

Webhook Token Authentication

Webhook authentication is a hook for verifying bearer tokens.

• --authentication-token-webhook-config-file a configuration file describing how to access the remote webhook service.
• --authentication-token-webhook-cache-ttl how long to cache authentication decisions. Defaults to two minutes.
• --authentication-token-webhook-version determines whether to use authentication.k8s.io/v1beta1 or authentication.k8s.io/v1 TokenReview objects to send/receive information from the webhook. Defaults to v1beta1.

The configuration file uses the kubeconfig file format. Within the file, clusters refers to the remote service and users refers to the API server webhook. An example would be:

# Kubernetes API version
apiVersion: v1
# kind of the API object
kind: Config
# clusters refers to the remote service.
clusters:
  - name: name-of-remote-authn-service
    cluster:
      certificate-authority: /path/to/ca.pem         # CA for verifying the remote service.
      server: https://authn.example.com/authenticate # URL of remote service to query. 'https' recommended for production.

# users refers to the API server's webhook configuration.
users:
  - name: name-of-api-server
    user:
      client-certificate: /path/to/cert.pem # cert for the webhook plugin to use
      client-key: /path/to/key.pem          # key matching the cert

# kubeconfig files require a context. Provide one for the API server.
current-context: webhook
contexts:
- context:
    cluster: name-of-remote-authn-service
    user: name-of-api-server
  name: webhook

When a client attempts to authenticate with the API server using a bearer token as discussed above, the authentication webhook POSTs a JSON-serialized TokenReview object containing the token to the remote service.

Note that webhook API objects are subject to the same versioning compatibility rules as other Kubernetes API objects. Implementers should check the apiVersion field of the request to ensure correct deserialization, and must respond with a TokenReview object of the same version as the request.

• authentication.k8s.io/v1
• authentication.k8s.io/v1beta1

{
  "apiVersion": "authentication.k8s.io/v1",
  "kind": "TokenReview",
  "spec": {
    # Opaque bearer token sent to the API server
    "token": "014fbff9a07c...",

    # Optional list of the audience identifiers for the server the token was presented to.
    # Audience-aware token authenticators (for example, OIDC token authenticators)
    # should verify the token was intended for at least one of the audiences in this list,
    # and return the intersection of this list and the valid audiences for the token in the response status.
    # This ensures the token is valid to authenticate to the server it was presented to.
    # If no audiences are provided, the token should be validated to authenticate to the Kubernetes API server.
    "audiences": ["https://myserver.example.com", "https://myserver.internal.example.com"]
  }
}

{
  "apiVersion": "authentication.k8s.io/v1beta1",
  "kind": "TokenReview",
  "spec": {
    # Opaque bearer token sent to the API server
    "token": "014fbff9a07c...",

    # Optional list of the audience identifiers for the server the token was presented to.
    # Audience-aware token authenticators (for example, OIDC token authenticators)
    # should verify the token was intended for at least one of the audiences in this list,
    # and return the intersection of this list and the valid audiences for the token in the response status.
    # This ensures the token is valid to authenticate to the server it was presented to.
    # If no audiences are provided, the token should be validated to authenticate to the Kubernetes API server.
    "audiences": ["https://myserver.example.com", "https://myserver.internal.example.com"]
  }
}

The remote service is expected to fill the status field of the request to indicate the success of the login. The response body's spec field is ignored and may be omitted. The remote service must return a response using the same TokenReview API version that it received. A successful validation of the bearer token would return:

• authentication.k8s.io/v1
• authentication.k8s.io/v1beta1

{
  "apiVersion": "authentication.k8s.io/v1",
  "kind": "TokenReview",
  "status": {
    "authenticated": true,
    "user": {
      # Required
      "username": "janedoe@example.com",
      # Optional
      "uid": "42",
      # Optional group memberships
      "groups": ["developers", "qa"],
      # Optional additional information provided by the authenticator.
      # This should not contain confidential data, as it can be recorded in logs
      # or API objects, and is made available to admission webhooks.
      "extra": {
        "extrafield1": [
          "extravalue1",
          "extravalue2"
        ]
      }
    },
    # Optional list audience-aware token authenticators can return,
    # containing the audiences from the `spec.audiences` list for which the provided token was valid.
    # If this is omitted, the token is considered to be valid to authenticate to the Kubernetes API server.
    "audiences": ["https://myserver.example.com"]
  }
}

{
  "apiVersion": "authentication.k8s.io/v1beta1",
  "kind": "TokenReview",
  "status": {
    "authenticated": true,
    "user": {
      # Required
      "username": "janedoe@example.com",
      # Optional
      "uid": "42",
      # Optional group memberships
      "groups": ["developers", "qa"],
      # Optional additional information provided by the authenticator.
      # This should not contain confidential data, as it can be recorded in logs
      # or API objects, and is made available to admission webhooks.
      "extra": {
        "extrafield1": [
          "extravalue1",
          "extravalue2"
        ]
      }
    },
    # Optional list audience-aware token authenticators can return,
    # containing the audiences from the `spec.audiences` list for which the provided token was valid.
    # If this is omitted, the token is considered to be valid to authenticate to the Kubernetes API server.
    "audiences": ["https://myserver.example.com"]
  }
}

An unsuccessful request would return:

• authentication.k8s.io/v1
• authentication.k8s.io/v1beta1

{
  "apiVersion": "authentication.k8s.io/v1",
  "kind": "TokenReview",
  "status": {
    "authenticated": false,
    # Optionally include details about why authentication failed.
    # If no error is provided, the API will return a generic Unauthorized message.
    # The error field is ignored when authenticated=true.
    "error": "Credentials are expired"
  }
}

{
  "apiVersion": "authentication.k8s.io/v1beta1",
  "kind": "TokenReview",
  "status": {
    "authenticated": false,
    # Optionally include details about why authentication failed.
    # If no error is provided, the API will return a generic Unauthorized message.
    # The error field is ignored when authenticated=true.
    "error": "Credentials are expired"
  }
}

Authenticating Proxy

The API server can be configured to identify users from request header values, such as X-Remote-User. It is designed for use in combination with an authenticating proxy, which sets the request header value.

• --requestheader-username-headers Required, case-insensitive. Header names to check, in order, for the user identity. The first header containing a value is used as the username.
• --requestheader-group-headers 1.6+. Optional, case-insensitive. "X-Remote-Group" is suggested. Header names to check, in order, for the user's groups. All values in all specified headers are used as group names.
• --requestheader-extra-headers-prefix 1.6+. Optional, case-insensitive. "X-Remote-Extra-" is suggested. Header prefixes to look for to determine extra information about the user (typically used by the configured authorization plugin). Any headers beginning with any of the specified prefixes have the prefix removed. The remainder of the header name is lowercased and percent-decoded and becomes the extra key, and the header value is the extra value.

For example, with this configuration:

--requestheader-username-headers=X-Remote-User
--requestheader-group-headers=X-Remote-Group
--requestheader-extra-headers-prefix=X-Remote-Extra-

this request:

GET / HTTP/1.1
X-Remote-User: fido
X-Remote-Group: dogs
X-Remote-Group: dachshunds
X-Remote-Extra-Acme.com%2Fproject: some-project
X-Remote-Extra-Scopes: openid
X-Remote-Extra-Scopes: profile

would result in this user info:

name: fido
groups:
- dogs
- dachshunds
extra:
  acme.com/project:
  - some-project
  scopes:
  - openid
  - profile

In order to prevent header spoofing, the authenticating proxy is required to present a valid client certificate to the API server for validation against the specified CA before the request headers are checked. WARNING: do not reuse a CA that is used in a different context unless you understand the risks and the mechanisms to protect the CA's usage.

• --requestheader-client-ca-file Required. PEM-encoded certificate bundle. A valid client certificate must be presented and validated against the certificate authorities in the specified file before the request headers are checked for user names.
• --requestheader-allowed-names Optional. List of Common Name values (CNs). If set, a valid client certificate with a CN in the specified list must be presented before the request headers are checked for user names. If empty, any CN is allowed.

Anonymous requests

When enabled, requests that are not rejected by other configured authentication methods are treated as anonymous requests, and given a username of system:anonymous and a group of system:unauthenticated.

For example, on a server with token authentication configured, and anonymous access enabled, a request providing an invalid bearer token would receive a 401 Unauthorized error. A request providing no bearer token would be treated as an anonymous request.

In 1.5.1-1.5.x, anonymous access is disabled by default, and can be enabled by passing the --anonymous-auth=true option to the API server.

In 1.6+, anonymous access is enabled by default if an authorization mode other than AlwaysAllow is used, and can be disabled by passing the --anonymous-auth=false option to the API server. Starting in 1.6, the ABAC and RBAC authorizers require explicit authorization of the system:anonymous user or the system:unauthenticated group, so legacy policy rules that grant access to the * user or * group do not include anonymous users.

Anonymous Authenticator Configuration

The AuthenticationConfiguration can be used to configure the anonymous authenticator. If you set the anonymous field in the AuthenticationConfiguration file then you cannot set the --anonymous-auth flag.

The main advantage of configuring anonymous authenticator using the authentication configuration file is that in addition to enabling and disabling anonymous authentication you can also configure which endpoints support anonymous authentication.

A sample authentication configuration file is below:

---
#
# CAUTION: this is an example configuration.
#          Do not use this for your own cluster!
#
apiVersion: apiserver.config.k8s.io/v1beta1
kind: AuthenticationConfiguration
anonymous:
  enabled: true
  conditions:
  - path: /livez
  - path: /readyz
  - path: /healthz

In the configuration above only the /livez, /readyz and /healthz endpoints are reachable by anonymous requests. Any other endpoints will not be reachable even if it is allowed by RBAC configuration.

User impersonation

A user can act as another user through impersonation headers. These let requests manually override the user info a request authenticates as. For example, an admin could use this feature to debug an authorization policy by temporarily impersonating another user and seeing if a request was denied.

Impersonation requests first authenticate as the requesting user, then switch to the impersonated user info.

• A user makes an API call with their credentials and impersonation headers.
• API server authenticates the user.
• API server ensures the authenticated users have impersonation privileges.
• Request user info is replaced with impersonation values.
• Request is evaluated, authorization acts on impersonated user info.

The following HTTP headers can be used to performing an impersonation request:

• Impersonate-User: The username to act as.
• Impersonate-Group: A group name to act as. Can be provided multiple times to set multiple groups. Optional. Requires "Impersonate-User".
• Impersonate-Extra-( extra name ): A dynamic header used to associate extra fields with the user. Optional. Requires "Impersonate-User". In order to be preserved consistently, ( extra name ) must be lower-case, and any characters which aren't legal in HTTP header labels MUST be utf8 and percent-encoded.
• Impersonate-Uid: A unique identifier that represents the user being impersonated. Optional. Requires "Impersonate-User". Kubernetes does not impose any format requirements on this string.

An example of the impersonation headers used when impersonating a user with groups:

Impersonate-User: jane.doe@example.com
Impersonate-Group: developers
Impersonate-Group: admins

An example of the impersonation headers used when impersonating a user with a UID and extra fields:

Impersonate-User: jane.doe@example.com
Impersonate-Extra-dn: cn=jane,ou=engineers,dc=example,dc=com
Impersonate-Extra-acme.com%2Fproject: some-project
Impersonate-Extra-scopes: view
Impersonate-Extra-scopes: development
Impersonate-Uid: 06f6ce97-e2c5-4ab8-7ba5-7654dd08d52b

When using kubectl set the --as flag to configure the Impersonate-User header, set the --as-group flag to configure the Impersonate-Group header.

kubectl drain mynode

Error from server (Forbidden): User "clark" cannot get nodes at the cluster scope. (get nodes mynode)

Set the --as and --as-group flag:

kubectl drain mynode --as=superman --as-group=system:masters

node/mynode cordoned
node/mynode drained

To impersonate a user, group, user identifier (UID) or extra fields, the impersonating user must have the ability to perform the "impersonate" verb on the kind of attribute being impersonated ("user", "group", "uid", etc.). For clusters that enable the RBAC authorization plugin, the following ClusterRole encompasses the rules needed to set user and group impersonation headers:

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: impersonator
rules:
- apiGroups: [""]
  resources: ["users", "groups", "serviceaccounts"]
  verbs: ["impersonate"]

For impersonation, extra fields and impersonated UIDs are both under the "authentication.k8s.io" apiGroup. Extra fields are evaluated as sub-resources of the resource "userextras". To allow a user to use impersonation headers for the extra field "scopes" and for UIDs, a user should be granted the following role:

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: scopes-and-uid-impersonator
rules:
# Can set "Impersonate-Extra-scopes" header and the "Impersonate-Uid" header.
- apiGroups: ["authentication.k8s.io"]
  resources: ["userextras/scopes", "uids"]
  verbs: ["impersonate"]

The values of impersonation headers can also be restricted by limiting the set of resourceNames a resource can take.

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: limited-impersonator
rules:
# Can impersonate the user "jane.doe@example.com"
- apiGroups: [""]
  resources: ["users"]
  verbs: ["impersonate"]
  resourceNames: ["jane.doe@example.com"]

# Can impersonate the groups "developers" and "admins"
- apiGroups: [""]
  resources: ["groups"]
  verbs: ["impersonate"]
  resourceNames: ["developers","admins"]

# Can impersonate the extras field "scopes" with the values "view" and "development"
- apiGroups: ["authentication.k8s.io"]
  resources: ["userextras/scopes"]
  verbs: ["impersonate"]
  resourceNames: ["view", "development"]

# Can impersonate the uid "06f6ce97-e2c5-4ab8-7ba5-7654dd08d52b"
- apiGroups: ["authentication.k8s.io"]
  resources: ["uids"]
  verbs: ["impersonate"]
  resourceNames: ["06f6ce97-e2c5-4ab8-7ba5-7654dd08d52b"]

client-go credential plugins

k8s.io/client-go and tools using it such as kubectl and kubelet are able to execute an external command to receive user credentials.

This feature is intended for client side integrations with authentication protocols not natively supported by k8s.io/client-go (LDAP, Kerberos, OAuth2, SAML, etc.). The plugin implements the protocol specific logic, then returns opaque credentials to use. Almost all credential plugin use cases require a server side component with support for the webhook token authenticator to interpret the credential format produced by the client plugin.

Example use case

In a hypothetical use case, an organization would run an external service that exchanges LDAP credentials for user specific, signed tokens. The service would also be capable of responding to webhook token authenticator requests to validate the tokens. Users would be required to install a credential plugin on their workstation.

To authenticate against the API:

• The user issues a kubectl command.
• Credential plugin prompts the user for LDAP credentials, exchanges credentials with external service for a token.
• Credential plugin returns token to client-go, which uses it as a bearer token against the API server.
• API server uses the webhook token authenticator to submit a TokenReview to the external service.
• External service verifies the signature on the token and returns the user's username and groups.

Configuration

Credential plugins are configured through kubectl config files as part of the user fields.

• client.authentication.k8s.io/v1
• client.authentication.k8s.io/v1beta1

apiVersion: v1
kind: Config
users:
- name: my-user
  user:
    exec:
      # Command to execute. Required.
      command: "example-client-go-exec-plugin"

      # API version to use when decoding the ExecCredentials resource. Required.
      #
      # The API version returned by the plugin MUST match the version listed here.
      #
      # To integrate with tools that support multiple versions (such as client.authentication.k8s.io/v1beta1),
      # set an environment variable, pass an argument to the tool that indicates which version the exec plugin expects,
      # or read the version from the ExecCredential object in the KUBERNETES_EXEC_INFO environment variable.
      apiVersion: "client.authentication.k8s.io/v1"

      # Environment variables to set when executing the plugin. Optional.
      env:
      - name: "FOO"
        value: "bar"

      # Arguments to pass when executing the plugin. Optional.
      args:
      - "arg1"
      - "arg2"

      # Text shown to the user when the executable doesn't seem to be present. Optional.
      installHint: |
        example-client-go-exec-plugin is required to authenticate
        to the current cluster.  It can be installed:

        On macOS: brew install example-client-go-exec-plugin

        On Ubuntu: apt-get install example-client-go-exec-plugin

        On Fedora: dnf install example-client-go-exec-plugin

        ...        

      # Whether or not to provide cluster information, which could potentially contain
      # very large CA data, to this exec plugin as a part of the KUBERNETES_EXEC_INFO
      # environment variable.
      provideClusterInfo: true

      # The contract between the exec plugin and the standard input I/O stream. If the
      # contract cannot be satisfied, this plugin will not be run and an error will be
      # returned. Valid values are "Never" (this exec plugin never uses standard input),
      # "IfAvailable" (this exec plugin wants to use standard input if it is available),
      # or "Always" (this exec plugin requires standard input to function). Required.
      interactiveMode: Never
clusters:
- name: my-cluster
  cluster:
    server: "https://172.17.4.100:6443"
    certificate-authority: "/etc/kubernetes/ca.pem"
    extensions:
    - name: client.authentication.k8s.io/exec # reserved extension name for per cluster exec config
      extension:
        arbitrary: config
        this: can be provided via the KUBERNETES_EXEC_INFO environment variable upon setting provideClusterInfo
        you: ["can", "put", "anything", "here"]
contexts:
- name: my-cluster
  context:
    cluster: my-cluster
    user: my-user
current-context: my-cluster

apiVersion: v1
kind: Config
users:
- name: my-user
  user:
    exec:
      # Command to execute. Required.
      command: "example-client-go-exec-plugin"

      # API version to use when decoding the ExecCredentials resource. Required.
      #
      # The API version returned by the plugin MUST match the version listed here.
      #
      # To integrate with tools that support multiple versions (such as client.authentication.k8s.io/v1),
      # set an environment variable, pass an argument to the tool that indicates which version the exec plugin expects,
      # or read the version from the ExecCredential object in the KUBERNETES_EXEC_INFO environment variable.
      apiVersion: "client.authentication.k8s.io/v1beta1"

      # Environment variables to set when executing the plugin. Optional.
      env:
      - name: "FOO"
        value: "bar"

      # Arguments to pass when executing the plugin. Optional.
      args:
      - "arg1"
      - "arg2"

      # Text shown to the user when the executable doesn't seem to be present. Optional.
      installHint: |
        example-client-go-exec-plugin is required to authenticate
        to the current cluster.  It can be installed:

        On macOS: brew install example-client-go-exec-plugin

        On Ubuntu: apt-get install example-client-go-exec-plugin

        On Fedora: dnf install example-client-go-exec-plugin

        ...        

      # Whether or not to provide cluster information, which could potentially contain
      # very large CA data, to this exec plugin as a part of the KUBERNETES_EXEC_INFO
      # environment variable.
      provideClusterInfo: true

      # The contract between the exec plugin and the standard input I/O stream. If the
      # contract cannot be satisfied, this plugin will not be run and an error will be
      # returned. Valid values are "Never" (this exec plugin never uses standard input),
      # "IfAvailable" (this exec plugin wants to use standard input if it is available),
      # or "Always" (this exec plugin requires standard input to function). Optional.
      # Defaults to "IfAvailable".
      interactiveMode: Never
clusters:
- name: my-cluster
  cluster:
    server: "https://172.17.4.100:6443"
    certificate-authority: "/etc/kubernetes/ca.pem"
    extensions:
    - name: client.authentication.k8s.io/exec # reserved extension name for per cluster exec config
      extension:
        arbitrary: config
        this: can be provided via the KUBERNETES_EXEC_INFO environment variable upon setting provideClusterInfo
        you: ["can", "put", "anything", "here"]
contexts:
- name: my-cluster
  context:
    cluster: my-cluster
    user: my-user
current-context: my-cluster

Relative command paths are interpreted as relative to the directory of the config file. If KUBECONFIG is set to /home/jane/kubeconfig and the exec command is ./bin/example-client-go-exec-plugin, the binary /home/jane/bin/example-client-go-exec-plugin is executed.

- name: my-user
  user:
    exec:
      # Path relative to the directory of the kubeconfig
      command: "./bin/example-client-go-exec-plugin"
      apiVersion: "client.authentication.k8s.io/v1"
      interactiveMode: Never

Input and output formats

The executed command prints an ExecCredential object to stdout. k8s.io/client-go authenticates against the Kubernetes API using the returned credentials in the status. The executed command is passed an ExecCredential object as input via the KUBERNETES_EXEC_INFO environment variable. This input contains helpful information like the expected API version of the returned ExecCredential object and whether or not the plugin can use stdin to interact with the user.

When run from an interactive session (i.e., a terminal), stdin can be exposed directly to the plugin. Plugins should use the spec.interactive field of the input ExecCredential object from the KUBERNETES_EXEC_INFO environment variable in order to determine if stdin has been provided. A plugin's stdin requirements (i.e., whether stdin is optional, strictly required, or never used in order for the plugin to run successfully) is declared via the user.exec.interactiveMode field in the kubeconfig (see table below for valid values). The user.exec.interactiveMode field is optional in client.authentication.k8s.io/v1beta1 and required in client.authentication.k8s.io/v1.

To use bearer token credentials, the plugin returns a token in the status of the ExecCredential

• client.authentication.k8s.io/v1
• client.authentication.k8s.io/v1beta1

{
  "apiVersion": "client.authentication.k8s.io/v1",
  "kind": "ExecCredential",
  "status": {
    "token": "my-bearer-token"
  }
}

{
  "apiVersion": "client.authentication.k8s.io/v1beta1",
  "kind": "ExecCredential",
  "status": {
    "token": "my-bearer-token"
  }
}

Alternatively, a PEM-encoded client certificate and key can be returned to use TLS client auth. If the plugin returns a different certificate and key on a subsequent call, k8s.io/client-go will close existing connections with the server to force a new TLS handshake.

If specified, clientKeyData and clientCertificateData must both must be present.

clientCertificateData may contain additional intermediate certificates to send to the server.

• client.authentication.k8s.io/v1
• client.authentication.k8s.io/v1beta1

{
  "apiVersion": "client.authentication.k8s.io/v1",
  "kind": "ExecCredential",
  "status": {
    "clientCertificateData": "-----BEGIN CERTIFICATE-----\n...\n-----END CERTIFICATE-----",
    "clientKeyData": "-----BEGIN RSA PRIVATE KEY-----\n...\n-----END RSA PRIVATE KEY-----"
  }
}

{
  "apiVersion": "client.authentication.k8s.io/v1beta1",
  "kind": "ExecCredential",
  "status": {
    "clientCertificateData": "-----BEGIN CERTIFICATE-----\n...\n-----END CERTIFICATE-----",
    "clientKeyData": "-----BEGIN RSA PRIVATE KEY-----\n...\n-----END RSA PRIVATE KEY-----"
  }
}

Optionally, the response can include the expiry of the credential formatted as a RFC 3339 timestamp.

Presence or absence of an expiry has the following impact:

• If an expiry is included, the bearer token and TLS credentials are cached until the expiry time is reached, or if the server responds with a 401 HTTP status code, or when the process exits.
• If an expiry is omitted, the bearer token and TLS credentials are cached until the server responds with a 401 HTTP status code or until the process exits.

• client.authentication.k8s.io/v1
• client.authentication.k8s.io/v1beta1

{
  "apiVersion": "client.authentication.k8s.io/v1",
  "kind": "ExecCredential",
  "status": {
    "token": "my-bearer-token",
    "expirationTimestamp": "2018-03-05T17:30:20-08:00"
  }
}

{
  "apiVersion": "client.authentication.k8s.io/v1beta1",
  "kind": "ExecCredential",
  "status": {
    "token": "my-bearer-token",
    "expirationTimestamp": "2018-03-05T17:30:20-08:00"
  }
}

To enable the exec plugin to obtain cluster-specific information, set provideClusterInfo on the user.exec field in the kubeconfig. The plugin will then be supplied this cluster-specific information in the KUBERNETES_EXEC_INFO environment variable. Information from this environment variable can be used to perform cluster-specific credential acquisition logic. The following ExecCredential manifest describes a cluster information sample.

• client.authentication.k8s.io/v1
• client.authentication.k8s.io/v1beta1

{
  "apiVersion": "client.authentication.k8s.io/v1",
  "kind": "ExecCredential",
  "spec": {
    "cluster": {
      "server": "https://172.17.4.100:6443",
      "certificate-authority-data": "LS0t...",
      "config": {
        "arbitrary": "config",
        "this": "can be provided via the KUBERNETES_EXEC_INFO environment variable upon setting provideClusterInfo",
        "you": ["can", "put", "anything", "here"]
      }
    },
    "interactive": true
  }
}

{
  "apiVersion": "client.authentication.k8s.io/v1beta1",
  "kind": "ExecCredential",
  "spec": {
    "cluster": {
      "server": "https://172.17.4.100:6443",
      "certificate-authority-data": "LS0t...",
      "config": {
        "arbitrary": "config",
        "this": "can be provided via the KUBERNETES_EXEC_INFO environment variable upon setting provideClusterInfo",
        "you": ["can", "put", "anything", "here"]
      }
    },
    "interactive": true
  }
}

API access to authentication information for a client

If your cluster has the API enabled, you can use the SelfSubjectReview API to find out how your Kubernetes cluster maps your authentication information to identify you as a client. This works whether you are authenticating as a user (typically representing a real person) or as a ServiceAccount.

SelfSubjectReview objects do not have any configurable fields. On receiving a request, the Kubernetes API server fills the status with the user attributes and returns it to the user.

Request example (the body would be a SelfSubjectReview):

POST /apis/authentication.k8s.io/v1/selfsubjectreviews

{
  "apiVersion": "authentication.k8s.io/v1",
  "kind": "SelfSubjectReview"
}

Response example:

{
  "apiVersion": "authentication.k8s.io/v1",
  "kind": "SelfSubjectReview",
  "status": {
    "userInfo": {
      "name": "jane.doe",
      "uid": "b6c7cfd4-f166-11ec-8ea0-0242ac120002",
      "groups": [
        "viewers",
        "editors",
        "system:authenticated"
      ],
      "extra": {
        "provider_id": ["token.company.example"]
      }
    }
  }
}

For convenience, the kubectl auth whoami command is present. Executing this command will produce the following output (yet different user attributes will be shown):

• Simple output example

  ATTRIBUTE         VALUE
  Username          jane.doe
  Groups            [system:authenticated]
  

• Complex example including extra attributes

  ATTRIBUTE         VALUE
  Username          jane.doe
  UID               b79dbf30-0c6a-11ed-861d-0242ac120002
  Groups            [students teachers system:authenticated]
  Extra: skills     [reading learning]
  Extra: subjects   [math sports]
  

By providing the output flag, it is also possible to print the JSON or YAML representation of the result:

• JSON
• YAML

{
  "apiVersion": "authentication.k8s.io/v1",
  "kind": "SelfSubjectReview",
  "status": {
    "userInfo": {
      "username": "jane.doe",
      "uid": "b79dbf30-0c6a-11ed-861d-0242ac120002",
      "groups": [
        "students",
        "teachers",
        "system:authenticated"
      ],
      "extra": {
        "skills": [
          "reading",
          "learning"
        ],
        "subjects": [
          "math",
          "sports"
        ]
      }
    }
  }
}

apiVersion: authentication.k8s.io/v1
kind: SelfSubjectReview
status:
  userInfo:
    username: jane.doe
    uid: b79dbf30-0c6a-11ed-861d-0242ac120002
    groups:
    - students
    - teachers
    - system:authenticated
    extra:
      skills:
      - reading
      - learning
      subjects:
      - math
      - sports

This feature is extremely useful when a complicated authentication flow is used in a Kubernetes cluster, for example, if you use webhook token authentication or authenticating proxy.

By default, all authenticated users can create SelfSubjectReview objects when the APISelfSubjectReview feature is enabled. It is allowed by the system:basic-user cluster role.

What's next

• Read the client authentication reference (v1beta1)
• Read the client authentication reference (v1)

2 - Authenticating with Bootstrap Tokens

Bootstrap tokens are a simple bearer token that is meant to be used when creating new clusters or joining new nodes to an existing cluster. It was built to support kubeadm, but can be used in other contexts for users that wish to start clusters without kubeadm. It is also built to work, via RBAC policy, with the kubelet TLS Bootstrapping system.

Bootstrap Tokens Overview

Bootstrap Tokens are defined with a specific type (bootstrap.kubernetes.io/token) of secrets that lives in the kube-system namespace. These Secrets are then read by the Bootstrap Authenticator in the API Server. Expired tokens are removed with the TokenCleaner controller in the Controller Manager. The tokens are also used to create a signature for a specific ConfigMap used in a "discovery" process through a BootstrapSigner controller.

Token Format

Bootstrap Tokens take the form of abcdef.0123456789abcdef. More formally, they must match the regular expression [a-z0-9]{6}\.[a-z0-9]{16}.

The first part of the token is the "Token ID" and is considered public information. It is used when referring to a token without leaking the secret part used for authentication. The second part is the "Token Secret" and should only be shared with trusted parties.

Enabling Bootstrap Token Authentication

The Bootstrap Token authenticator can be enabled using the following flag on the API server:

--enable-bootstrap-token-auth

When enabled, bootstrapping tokens can be used as bearer token credentials to authenticate requests against the API server.

Authorization: Bearer 07401b.f395accd246ae52d

Tokens authenticate as the username system:bootstrap:<token id> and are members of the group system:bootstrappers. Additional groups may be specified in the token's Secret.

Expired tokens can be deleted automatically by enabling the tokencleaner controller on the controller manager.

--controllers=*,tokencleaner

Bootstrap Token Secret Format

Each valid token is backed by a secret in the kube-system namespace. You can find the full design doc here.

Here is what the secret looks like.

apiVersion: v1
kind: Secret
metadata:
  # Name MUST be of form "bootstrap-token-<token id>"
  name: bootstrap-token-07401b
  namespace: kube-system

# Type MUST be 'bootstrap.kubernetes.io/token'
type: bootstrap.kubernetes.io/token
stringData:
  # Human readable description. Optional.
  description: "The default bootstrap token generated by 'kubeadm init'."

  # Token ID and secret. Required.
  token-id: 07401b
  token-secret: f395accd246ae52d

  # Expiration. Optional.
  expiration: 2017-03-10T03:22:11Z

  # Allowed usages.
  usage-bootstrap-authentication: "true"
  usage-bootstrap-signing: "true"

  # Extra groups to authenticate the token as. Must start with "system:bootstrappers:"
  auth-extra-groups: system:bootstrappers:worker,system:bootstrappers:ingress

The type of the secret must be bootstrap.kubernetes.io/token and the name must be bootstrap-token-<token id>. It must also exist in the kube-system namespace.

The usage-bootstrap-* members indicate what this secret is intended to be used for. A value must be set to true to be enabled.

• usage-bootstrap-authentication indicates that the token can be used to authenticate to the API server as a bearer token.
• usage-bootstrap-signing indicates that the token may be used to sign the cluster-info ConfigMap as described below.

The expiration field controls the expiry of the token. Expired tokens are rejected when used for authentication and ignored during ConfigMap signing. The expiry value is encoded as an absolute UTC time using RFC3339. Enable the tokencleaner controller to automatically delete expired tokens.

Token Management with kubeadm

You can use the kubeadm tool to manage tokens on a running cluster. See the kubeadm token docs for details.

ConfigMap Signing

In addition to authentication, the tokens can be used to sign a ConfigMap. This is used early in a cluster bootstrap process before the client trusts the API server. The signed ConfigMap can be authenticated by the shared token.

Enable ConfigMap signing by enabling the bootstrapsigner controller on the Controller Manager.

--controllers=*,bootstrapsigner

The ConfigMap that is signed is cluster-info in the kube-public namespace. The typical flow is that a client reads this ConfigMap while unauthenticated and ignoring TLS errors. It then validates the payload of the ConfigMap by looking at a signature embedded in the ConfigMap.

The ConfigMap may look like this:

apiVersion: v1
kind: ConfigMap
metadata:
  name: cluster-info
  namespace: kube-public
data:
  jws-kubeconfig-07401b: eyJhbGciOiJIUzI1NiIsImtpZCI6IjA3NDAxYiJ9..tYEfbo6zDNo40MQE07aZcQX2m3EB2rO3NuXtxVMYm9U
  kubeconfig: |
    apiVersion: v1
    clusters:
    - cluster:
        certificate-authority-data: <really long certificate data>
        server: https://10.138.0.2:6443
      name: ""
    contexts: []
    current-context: ""
    kind: Config
    preferences: {}
    users: []    

The kubeconfig member of the ConfigMap is a config file with only the cluster information filled out. The key thing being communicated here is the certificate-authority-data. This may be expanded in the future.

The signature is a JWS signature using the "detached" mode. To validate the signature, the user should encode the kubeconfig payload according to JWS rules (base64 encoded while discarding any trailing =). That encoded payload is then used to form a whole JWS by inserting it between the 2 dots. You can verify the JWS using the HS256 scheme (HMAC-SHA256) with the full token (e.g. 07401b.f395accd246ae52d) as the shared secret. Users must verify that HS256 is used.

Consult the kubeadm implementation details section for more information.

3 - Authorization

Kubernetes authorization takes place following authentication. Usually, a client making a request must be authenticated (logged in) before its request can be allowed; however, Kubernetes also allows anonymous requests in some circumstances.

For an overview of how authorization fits into the wider context of API access control, read Controlling Access to the Kubernetes API.

Authorization verdicts

Kubernetes authorization of API requests takes place within the API server. The API server evaluates all of the request attributes against all policies, potentially also consulting external services, and then allows or denies the request.

All parts of an API request must be allowed by some authorization mechanism in order to proceed. In other words: access is denied by default.

When multiple authorization modules are configured, each is checked in sequence. If any authorizer approves or denies a request, that decision is immediately returned and no other authorizer is consulted. If all modules have no opinion on the request, then the request is denied. An overall deny verdict means that the API server rejects the request and responds with an HTTP 403 (Forbidden) status.

Request attributes used in authorization

Kubernetes reviews only the following API request attributes:

• user - The user string provided during authentication.
• group - The list of group names to which the authenticated user belongs.
• extra - A map of arbitrary string keys to string values, provided by the authentication layer.
• API - Indicates whether the request is for an API resource.
• Request path - Path to miscellaneous non-resource endpoints like /api or /healthz.
• API request verb - API verbs like get, list, create, update, patch, watch, delete, and deletecollection are used for resource requests. To determine the request verb for a resource API endpoint, see request verbs and authorization.
• HTTP request verb - Lowercased HTTP methods like get, post, put, and delete are used for non-resource requests.
• Resource - The ID or name of the resource that is being accessed (for resource requests only) -- For resource requests using get, update, patch, and delete verbs, you must provide the resource name.
• Subresource - The subresource that is being accessed (for resource requests only).
• Namespace - The namespace of the object that is being accessed (for namespaced resource requests only).
• API group - The API Group being accessed (for resource requests only). An empty string designates the core API group.

Request verbs and authorization

Non-resource requests

Requests to endpoints other than /api/v1/... or /apis/<group>/<version>/... are considered non-resource requests, and use the lower-cased HTTP method of the request as the verb. For example, making a GET request using HTTP to endpoints such as /api or /healthz would use get as the verb.

Resource requests

To determine the request verb for a resource API endpoint, Kubernetes maps the HTTP verb used and considers whether or not the request acts on an individual resource or on a collection of resources:

Kubernetes sometimes checks authorization for additional permissions using specialized verbs. For example:

• Special cases of authentication
  • impersonate verb on users, groups, and serviceaccounts in the core API group, and the userextras in the authentication.k8s.io API group.
• Authorization of CertificateSigningRequests
  • approve verb for CertificateSigningRequests, and update for revisions to existing approvals
• RBAC
  • bind and escalate verbs on roles and clusterroles resources in the rbac.authorization.k8s.io API group.

Authorization context

Kubernetes expects attributes that are common to REST API requests. This means that Kubernetes authorization works with existing organization-wide or cloud-provider-wide access control systems which may handle other APIs besides the Kubernetes API.

Authorization modes

The Kubernetes API server may authorize a request using one of several authorization modes:

AlwaysAllow

This mode allows all requests, which brings security risks. Use this authorization mode only if you do not require authorization for your API requests (for example, for testing).

AlwaysDeny

This mode blocks all requests. Use this authorization mode only for testing.

ABAC (attribute-based access control)

Kubernetes ABAC mode defines an access control paradigm whereby access rights are granted to users through the use of policies which combine attributes together. The policies can use any type of attributes (user attributes, resource attributes, object, environment attributes, etc).

RBAC (role-based access control)

Kubernetes RBAC is a method of regulating access to computer or network resources based on the roles of individual users within an enterprise. In this context, access is the ability of an individual user to perform a specific task, such as view, create, or modify a file.
In this mode, Kubernetes uses the rbac.authorization.k8s.io API group to drive authorization decisions, allowing you to dynamically configure permission policies through the Kubernetes API.

Node

A special-purpose authorization mode that grants permissions to kubelets based on the pods they are scheduled to run. To learn more about the Node authorization mode, see Node Authorization.

Webhook

Kubernetes webhook mode for authorization makes a synchronous HTTP callout, blocking the request until the remote HTTP service responds to the query.You can write your own software to handle the callout, or use solutions from the ecosystem.

The system:masters group

The system:masters group is a built-in Kubernetes group that grants unrestricted access to the API server. Any user assigned to this group has full cluster administrator privileges, bypassing any authorization restrictions imposed by the RBAC or Webhook mechanisms. Avoid adding users to this group. If you do need to grant a user cluster-admin rights, you can create a ClusterRoleBinding to the built-in cluster-admin ClusterRole.

Authorization mode configuration

You can configure the Kubernetes API server's authorizer chain using either a configuration file only or command line arguments.

You have to pick one of the two configuration approaches; setting both --authorization-config path and configuring an authorization webhook using the --authorization-mode and --authorization-webhook-* command line arguments is not allowed. If you try this, the API server reports an error message during startup, then exits immediately.

The configuration file approach even allows you to specify CEL rules to pre-filter requests before they are dispatched to webhooks, helping you to prevent unnecessary invocations. The API server also automatically reloads the authorizer chain when the configuration file is modified.

You specify the path to the authorization configuration using the --authorization-config command line argument.

If you want to use command line arguments instead of a configuration file, that's also a valid and supported approach. Some authorization capabilities (for example: multiple webhooks, webhook failure policy, and pre-filter rules) are only available if you use an authorization configuration file.

Example configuration

---
#
# DO NOT USE THE CONFIG AS IS. THIS IS AN EXAMPLE.
#
apiVersion: apiserver.config.k8s.io/v1
kind: AuthorizationConfiguration
authorizers:
  - type: Webhook
    # Name used to describe the authorizer
    # This is explicitly used in monitoring machinery for metrics
    # Note:
    #   - Validation for this field is similar to how K8s labels are validated today.
    # Required, with no default
    name: webhook
    webhook:
      # The duration to cache 'authorized' responses from the webhook
      # authorizer.
      # Same as setting `--authorization-webhook-cache-authorized-ttl` flag
      # Default: 5m0s
      authorizedTTL: 30s
      # The duration to cache 'unauthorized' responses from the webhook
      # authorizer.
      # Same as setting `--authorization-webhook-cache-unauthorized-ttl` flag
      # Default: 30s
      unauthorizedTTL: 30s
      # Timeout for the webhook request
      # Maximum allowed is 30s.
      # Required, with no default.
      timeout: 3s
      # The API version of the authorization.k8s.io SubjectAccessReview to
      # send to and expect from the webhook.
      # Same as setting `--authorization-webhook-version` flag
      # Required, with no default
      # Valid values: v1beta1, v1
      subjectAccessReviewVersion: v1
      # MatchConditionSubjectAccessReviewVersion specifies the SubjectAccessReview
      # version the CEL expressions are evaluated against
      # Valid values: v1
      # Required, no default value
      matchConditionSubjectAccessReviewVersion: v1
      # Controls the authorization decision when a webhook request fails to
      # complete or returns a malformed response or errors evaluating
      # matchConditions.
      # Valid values:
      #   - NoOpinion: continue to subsequent authorizers to see if one of
      #     them allows the request
      #   - Deny: reject the request without consulting subsequent authorizers
      # Required, with no default.
      failurePolicy: Deny
      connectionInfo:
        # Controls how the webhook should communicate with the server.
        # Valid values:
        # - KubeConfigFile: use the file specified in kubeConfigFile to locate the
        #   server.
        # - InClusterConfig: use the in-cluster configuration to call the
        #   SubjectAccessReview API hosted by kube-apiserver. This mode is not
        #   allowed for kube-apiserver.
        type: KubeConfigFile
        # Path to KubeConfigFile for connection info
        # Required, if connectionInfo.Type is KubeConfigFile
        kubeConfigFile: /kube-system-authz-webhook.yaml
        # matchConditions is a list of conditions that must be met for a request to be sent to this
        # webhook. An empty list of matchConditions matches all requests.
        # There are a maximum of 64 match conditions allowed.
        #
        # The exact matching logic is (in order):
        #   1. If at least one matchCondition evaluates to FALSE, then the webhook is skipped.
        #   2. If ALL matchConditions evaluate to TRUE, then the webhook is called.
        #   3. If at least one matchCondition evaluates to an error (but none are FALSE):
        #      - If failurePolicy=Deny, then the webhook rejects the request
        #      - If failurePolicy=NoOpinion, then the error is ignored and the webhook is skipped
      matchConditions:
      # expression represents the expression which will be evaluated by CEL. Must evaluate to bool.
      # CEL expressions have access to the contents of the SubjectAccessReview in v1 version.
      # If version specified by subjectAccessReviewVersion in the request variable is v1beta1,
      # the contents would be converted to the v1 version before evaluating the CEL expression.
      #
      # Documentation on CEL: https://kubernetes.io/docs/reference/using-api/cel/
      #
      # only send resource requests to the webhook
      - expression: has(request.resourceAttributes)
      # only intercept requests to kube-system
      - expression: request.resourceAttributes.namespace == 'kube-system'
      # don't intercept requests from kube-system service accounts
      - expression: "!('system:serviceaccounts:kube-system' in request.groups)"
  - type: Node
    name: node
  - type: RBAC
    name: rbac
  - type: Webhook
    name: in-cluster-authorizer
    webhook:
      authorizedTTL: 5m
      unauthorizedTTL: 30s
      timeout: 3s
      subjectAccessReviewVersion: v1
      failurePolicy: NoOpinion
      connectionInfo:
        type: InClusterConfig

When configuring the authorizer chain using a configuration file, make sure all the control plane nodes have the same file contents. Take a note of the API server configuration when upgrading / downgrading your clusters. For example, if upgrading from Kubernetes 1.31 to Kubernetes 1.32, you would need to make sure the config file is in a format that Kubernetes 1.32 can understand, before you upgrade the cluster. If you downgrade to 1.31, you would need to set the configuration appropriately.

Authorization configuration and reloads

Kubernetes reloads the authorization configuration file when the API server observes a change to the file, and also on a 60 second schedule if no change events were observed.

Command line authorization mode configuration

You can use the following modes:

• --authorization-mode=ABAC (Attribute-based access control mode)
• --authorization-mode=RBAC (Role-based access control mode)
• --authorization-mode=Node (Node authorizer)
• --authorization-mode=Webhook (Webhook authorization mode)
• --authorization-mode=AlwaysAllow (always allows requests; carries security risks)
• --authorization-mode=AlwaysDeny (always denies requests)

You can choose more than one authorization mode; for example: --authorization-mode=Node,RBAC,Webhook

Kubernetes checks authorization modules based on the order that you specify them on the API server's command line, so an earlier module has higher priority to allow or deny a request.

You cannot combine the --authorization-mode command line argument with the --authorization-config command line argument used for configuring authorization using a local file.

For more information on command line arguments to the API server, read the kube-apiserver reference.

Privilege escalation via workload creation or edits

Users who can create/edit pods in a namespace, either directly or through an object that enables indirect workload management, may be able to escalate their privileges in that namespace. The potential routes to privilege escalation include Kubernetes API extensions and their associated controllers.

Escalation paths

There are different ways that an attacker or untrustworthy user could gain additional privilege within a namespace, if you allow them to run arbitrary Pods in that namespace:

• Mounting arbitrary Secrets in that namespace
  • Can be used to access confidential information meant for other workloads
  • Can be used to obtain a more privileged ServiceAccount's service account token
• Using arbitrary ServiceAccounts in that namespace
  • Can perform Kubernetes API actions as another workload (impersonation)
  • Can perform any privileged actions that ServiceAccount has
• Mounting or using ConfigMaps meant for other workloads in that namespace
  • Can be used to obtain information meant for other workloads, such as database host names.
• Mounting volumes meant for other workloads in that namespace
  • Can be used to obtain information meant for other workloads, and change it.

Checking API access

kubectl provides the auth can-i subcommand for quickly querying the API authorization layer. The command uses the SelfSubjectAccessReview API to determine if the current user can perform a given action, and works regardless of the authorization mode used.

kubectl auth can-i create deployments --namespace dev

The output is similar to this:

yes

kubectl auth can-i create deployments --namespace prod

The output is similar to this:

no

Administrators can combine this with user impersonation to determine what action other users can perform.

kubectl auth can-i list secrets --namespace dev --as dave

The output is similar to this:

no

Similarly, to check whether a ServiceAccount named dev-sa in Namespace dev can list Pods in the Namespace target:

kubectl auth can-i list pods \
    --namespace target \
    --as system:serviceaccount:dev:dev-sa

The output is similar to this:

yes

SelfSubjectAccessReview is part of the authorization.k8s.io API group, which exposes the API server authorization to external services. Other resources in this group include:

SubjectAccessReview

Access review for any user, not only the current one. Useful for delegating authorization decisions to the API server. For example, the kubelet and extension API servers use this to determine user access to their own APIs.

LocalSubjectAccessReview

Like SubjectAccessReview but restricted to a specific namespace.

SelfSubjectRulesReview

A review which returns the set of actions a user can perform within a namespace. Useful for users to quickly summarize their own access, or for UIs to hide/show actions.

These APIs can be queried by creating normal Kubernetes resources, where the response status field of the returned object is the result of the query. For example:

kubectl create -f - -o yaml << EOF
apiVersion: authorization.k8s.io/v1
kind: SelfSubjectAccessReview
spec:
  resourceAttributes:
    group: apps
    resource: deployments
    verb: create
    namespace: dev
EOF

The generated SelfSubjectAccessReview is similar to:

apiVersion: authorization.k8s.io/v1
kind: SelfSubjectAccessReview
metadata:
  creationTimestamp: null
spec:
  resourceAttributes:
    group: apps
    resource: deployments
    namespace: dev
    verb: create
status:
  allowed: true
  denied: false

What's next

• To learn more about Authentication, see Authentication.
• For an overview, read Controlling Access to the Kubernetes API.
• To learn more about Admission Control, see Using Admission Controllers.
• Read more about Common Expression Language in Kubernetes.

4 - Using RBAC Authorization

Role-based access control (RBAC) is a method of regulating access to computer or network resources based on the roles of individual users within your organization.

RBAC authorization uses the rbac.authorization.k8s.io API group to drive authorization decisions, allowing you to dynamically configure policies through the Kubernetes API.

To enable RBAC, start the API server with the --authorization-config flag set to a file that includes the RBAC authorizer; for example:

apiVersion: apiserver.config.k8s.io/v1
kind: AuthorizationConfiguration
authorizers:
  ...
  - type: RBAC
  ...

Or, start the API server with the --authorization-mode flag set to a comma-separated list that includes RBAC; for example:

kube-apiserver --authorization-mode=...,RBAC --other-options --more-options

API objects

The RBAC API declares four kinds of Kubernetes object: Role, ClusterRole, RoleBinding and ClusterRoleBinding. You can describe or amend the RBAC objects using tools such as kubectl, just like any other Kubernetes object.

Role and ClusterRole

An RBAC Role or ClusterRole contains rules that represent a set of permissions. Permissions are purely additive (there are no "deny" rules).

A Role always sets permissions within a particular namespace; when you create a Role, you have to specify the namespace it belongs in.

ClusterRole, by contrast, is a non-namespaced resource. The resources have different names (Role and ClusterRole) because a Kubernetes object always has to be either namespaced or not namespaced; it can't be both.

ClusterRoles have several uses. You can use a ClusterRole to:

1. define permissions on namespaced resources and be granted access within individual namespace(s)
2. define permissions on namespaced resources and be granted access across all namespaces
3. define permissions on cluster-scoped resources

If you want to define a role within a namespace, use a Role; if you want to define a role cluster-wide, use a ClusterRole.

Role example

Here's an example Role in the "default" namespace that can be used to grant read access to pods:

apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  namespace: default
  name: pod-reader
rules:
- apiGroups: [""] # "" indicates the core API group
  resources: ["pods"]
  verbs: ["get", "watch", "list"]

ClusterRole example

A ClusterRole can be used to grant the same permissions as a Role. Because ClusterRoles are cluster-scoped, you can also use them to grant access to:

• cluster-scoped resources (like nodes)

• non-resource endpoints (like /healthz)

• namespaced resources (like Pods), across all namespaces

  For example: you can use a ClusterRole to allow a particular user to run kubectl get pods --all-namespaces

Here is an example of a ClusterRole that can be used to grant read access to secrets in any particular namespace, or across all namespaces (depending on how it is bound):

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  # "namespace" omitted since ClusterRoles are not namespaced
  name: secret-reader
rules:
- apiGroups: [""]
  #
  # at the HTTP level, the name of the resource for accessing Secret
  # objects is "secrets"
  resources: ["secrets"]
  verbs: ["get", "watch", "list"]

The name of a Role or a ClusterRole object must be a valid path segment name.

RoleBinding and ClusterRoleBinding

A role binding grants the permissions defined in a role to a user or set of users. It holds a list of subjects (users, groups, or service accounts), and a reference to the role being granted. A RoleBinding grants permissions within a specific namespace whereas a ClusterRoleBinding grants that access cluster-wide.

A RoleBinding may reference any Role in the same namespace. Alternatively, a RoleBinding can reference a ClusterRole and bind that ClusterRole to the namespace of the RoleBinding. If you want to bind a ClusterRole to all the namespaces in your cluster, you use a ClusterRoleBinding.

The name of a RoleBinding or ClusterRoleBinding object must be a valid path segment name.

RoleBinding examples

Here is an example of a RoleBinding that grants the "pod-reader" Role to the user "jane" within the "default" namespace. This allows "jane" to read pods in the "default" namespace.

apiVersion: rbac.authorization.k8s.io/v1
# This role binding allows "jane" to read pods in the "default" namespace.
# You need to already have a Role named "pod-reader" in that namespace.
kind: RoleBinding
metadata:
  name: read-pods
  namespace: default
subjects:
# You can specify more than one "subject"
- kind: User
  name: jane # "name" is case sensitive
  apiGroup: rbac.authorization.k8s.io
roleRef:
  # "roleRef" specifies the binding to a Role / ClusterRole
  kind: Role #this must be Role or ClusterRole
  name: pod-reader # this must match the name of the Role or ClusterRole you wish to bind to
  apiGroup: rbac.authorization.k8s.io

A RoleBinding can also reference a ClusterRole to grant the permissions defined in that ClusterRole to resources inside the RoleBinding's namespace. This kind of reference lets you define a set of common roles across your cluster, then reuse them within multiple namespaces.

For instance, even though the following RoleBinding refers to a ClusterRole, "dave" (the subject, case sensitive) will only be able to read Secrets in the "development" namespace, because the RoleBinding's namespace (in its metadata) is "development".

apiVersion: rbac.authorization.k8s.io/v1
# This role binding allows "dave" to read secrets in the "development" namespace.
# You need to already have a ClusterRole named "secret-reader".
kind: RoleBinding
metadata:
  name: read-secrets
  #
  # The namespace of the RoleBinding determines where the permissions are granted.
  # This only grants permissions within the "development" namespace.
  namespace: development
subjects:
- kind: User
  name: dave # Name is case sensitive
  apiGroup: rbac.authorization.k8s.io
roleRef:
  kind: ClusterRole
  name: secret-reader
  apiGroup: rbac.authorization.k8s.io

ClusterRoleBinding example

To grant permissions across a whole cluster, you can use a ClusterRoleBinding. The following ClusterRoleBinding allows any user in the group "manager" to read secrets in any namespace.

apiVersion: rbac.authorization.k8s.io/v1
# This cluster role binding allows anyone in the "manager" group to read secrets in any namespace.
kind: ClusterRoleBinding
metadata:
  name: read-secrets-global
subjects:
- kind: Group
  name: manager # Name is case sensitive
  apiGroup: rbac.authorization.k8s.io
roleRef:
  kind: ClusterRole
  name: secret-reader
  apiGroup: rbac.authorization.k8s.io

After you create a binding, you cannot change the Role or ClusterRole that it refers to. If you try to change a binding's roleRef, you get a validation error. If you do want to change the roleRef for a binding, you need to remove the binding object and create a replacement.

There are two reasons for this restriction:

1. Making roleRef immutable allows granting someone update permission on an existing binding object, so that they can manage the list of subjects, without being able to change the role that is granted to those subjects.
2. A binding to a different role is a fundamentally different binding. Requiring a binding to be deleted/recreated in order to change the roleRef ensures the full list of subjects in the binding is intended to be granted the new role (as opposed to enabling or accidentally modifying only the roleRef without verifying all of the existing subjects should be given the new role's permissions).

The kubectl auth reconcile command-line utility creates or updates a manifest file containing RBAC objects, and handles deleting and recreating binding objects if required to change the role they refer to. See command usage and examples for more information.

Referring to resources

In the Kubernetes API, most resources are represented and accessed using a string representation of their object name, such as pods for a Pod. RBAC refers to resources using exactly the same name that appears in the URL for the relevant API endpoint. Some Kubernetes APIs involve a subresource, such as the logs for a Pod. A request for a Pod's logs looks like:

GET /api/v1/namespaces/{namespace}/pods/{name}/log

In this case, pods is the namespaced resource for Pod resources, and log is a subresource of pods. To represent this in an RBAC role, use a slash (/) to delimit the resource and subresource. To allow a subject to read pods and also access the log subresource for each of those Pods, you write:

apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  namespace: default
  name: pod-and-pod-logs-reader
rules:
- apiGroups: [""]
  resources: ["pods", "pods/log"]
  verbs: ["get", "list"]

You can also refer to resources by name for certain requests through the resourceNames list. When specified, requests can be restricted to individual instances of a resource. Here is an example that restricts its subject to only get or update a ConfigMap named my-configmap:

apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  namespace: default
  name: configmap-updater
rules:
- apiGroups: [""]
  #
  # at the HTTP level, the name of the resource for accessing ConfigMap
  # objects is "configmaps"
  resources: ["configmaps"]
  resourceNames: ["my-configmap"]
  verbs: ["update", "get"]

Rather than referring to individual resources, apiGroups, and verbs, you can use the wildcard * symbol to refer to all such objects. For nonResourceURLs, you can use the wildcard * as a suffix glob match. For resourceNames, an empty set means that everything is allowed. Here is an example that allows access to perform any current and future action on all current and future resources in the example.com API group. This is similar to the built-in cluster-admin role.

apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  namespace: default
  name: example.com-superuser # DO NOT USE THIS ROLE, IT IS JUST AN EXAMPLE
rules:
- apiGroups: ["example.com"]
  resources: ["*"]
  verbs: ["*"]

Aggregated ClusterRoles

You can aggregate several ClusterRoles into one combined ClusterRole. A controller, running as part of the cluster control plane, watches for ClusterRole objects with an aggregationRule set. The aggregationRule defines a label selector that the controller uses to match other ClusterRole objects that should be combined into the rules field of this one.

Here is an example aggregated ClusterRole:

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: monitoring
aggregationRule:
  clusterRoleSelectors:
  - matchLabels:
      rbac.example.com/aggregate-to-monitoring: "true"
rules: [] # The control plane automatically fills in the rules

If you create a new ClusterRole that matches the label selector of an existing aggregated ClusterRole, that change triggers adding the new rules into the aggregated ClusterRole. Here is an example that adds rules to the "monitoring" ClusterRole, by creating another ClusterRole labeled rbac.example.com/aggregate-to-monitoring: true.

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: monitoring-endpoints
  labels:
    rbac.example.com/aggregate-to-monitoring: "true"
# When you create the "monitoring-endpoints" ClusterRole,
# the rules below will be added to the "monitoring" ClusterRole.
rules:
- apiGroups: [""]
  resources: ["services", "endpointslices", "pods"]
  verbs: ["get", "list", "watch"]

The default user-facing roles use ClusterRole aggregation. This lets you, as a cluster administrator, include rules for custom resources, such as those served by CustomResourceDefinitions or aggregated API servers, to extend the default roles.

For example: the following ClusterRoles let the "admin" and "edit" default roles manage the custom resource named CronTab, whereas the "view" role can perform only read actions on CronTab resources. You can assume that CronTab objects are named "crontabs" in URLs as seen by the API server.

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: aggregate-cron-tabs-edit
  labels:
    # Add these permissions to the "admin" and "edit" default roles.
    rbac.authorization.k8s.io/aggregate-to-admin: "true"
    rbac.authorization.k8s.io/aggregate-to-edit: "true"
rules:
- apiGroups: ["stable.example.com"]
  resources: ["crontabs"]
  verbs: ["get", "list", "watch", "create", "update", "patch", "delete"]
---
kind: ClusterRole
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: aggregate-cron-tabs-view
  labels:
    # Add these permissions to the "view" default role.
    rbac.authorization.k8s.io/aggregate-to-view: "true"
rules:
- apiGroups: ["stable.example.com"]
  resources: ["crontabs"]
  verbs: ["get", "list", "watch"]

Role examples

The following examples are excerpts from Role or ClusterRole objects, showing only the rules section.

Allow reading "pods" resources in the core API Group:

rules:
- apiGroups: [""]
  #
  # at the HTTP level, the name of the resource for accessing Pod
  # objects is "pods"
  resources: ["pods"]
  verbs: ["get", "list", "watch"]

Allow reading/writing Deployments (at the HTTP level: objects with "deployments" in the resource part of their URL) in the "apps" API groups:

rules:
- apiGroups: ["apps"]
  #
  # at the HTTP level, the name of the resource for accessing Deployment
  # objects is "deployments"
  resources: ["deployments"]
  verbs: ["get", "list", "watch", "create", "update", "patch", "delete"]

Allow reading Pods in the core API group, as well as reading or writing Job resources in the "batch" API group:

rules:
- apiGroups: [""]
  #
  # at the HTTP level, the name of the resource for accessing Pod
  # objects is "pods"
  resources: ["pods"]
  verbs: ["get", "list", "watch"]
- apiGroups: ["batch"]
  #
  # at the HTTP level, the name of the resource for accessing Job
  # objects is "jobs"
  resources: ["jobs"]
  verbs: ["get", "list", "watch", "create", "update", "patch", "delete"]

Allow reading a ConfigMap named "my-config" (must be bound with a RoleBinding to limit to a single ConfigMap in a single namespace):

rules:
- apiGroups: [""]
  #
  # at the HTTP level, the name of the resource for accessing ConfigMap
  # objects is "configmaps"
  resources: ["configmaps"]
  resourceNames: ["my-config"]
  verbs: ["get"]

Allow reading the resource "nodes" in the core group (because a Node is cluster-scoped, this must be in a ClusterRole bound with a ClusterRoleBinding to be effective):

rules:
- apiGroups: [""]
  #
  # at the HTTP level, the name of the resource for accessing Node
  # objects is "nodes"
  resources: ["nodes"]
  verbs: ["get", "list", "watch"]

Allow GET and POST requests to the non-resource endpoint /healthz and all subpaths (must be in a ClusterRole bound with a ClusterRoleBinding to be effective):

rules:
- nonResourceURLs: ["/healthz", "/healthz/*"] # '*' in a nonResourceURL is a suffix glob match
  verbs: ["get", "post"]

Referring to subjects

A RoleBinding or ClusterRoleBinding binds a role to subjects. Subjects can be groups, users or ServiceAccounts.

Kubernetes represents usernames as strings. These can be: plain names, such as "alice"; email-style names, like "bob@example.com"; or numeric user IDs represented as a string. It is up to you as a cluster administrator to configure the authentication modules so that authentication produces usernames in the format you want.

In Kubernetes, Authenticator modules provide group information. Groups, like users, are represented as strings, and that string has no format requirements, other than that the prefix system: is reserved.

ServiceAccounts have names prefixed with system:serviceaccount:, and belong to groups that have names prefixed with system:serviceaccounts:.

RoleBinding examples

The following examples are RoleBinding excerpts that only show the subjects section.

For a user named alice@example.com:

subjects:
- kind: User
  name: "alice@example.com"
  apiGroup: rbac.authorization.k8s.io

For a group named frontend-admins:

subjects:
- kind: Group
  name: "frontend-admins"
  apiGroup: rbac.authorization.k8s.io

For the default service account in the "kube-system" namespace:

subjects:
- kind: ServiceAccount
  name: default
  namespace: kube-system

For all service accounts in the "qa" namespace:

subjects:
- kind: Group
  name: system:serviceaccounts:qa
  apiGroup: rbac.authorization.k8s.io

For all service accounts in any namespace:

subjects:
- kind: Group
  name: system:serviceaccounts
  apiGroup: rbac.authorization.k8s.io

For all authenticated users:

subjects:
- kind: Group
  name: system:authenticated
  apiGroup: rbac.authorization.k8s.io

For all unauthenticated users:

subjects:
- kind: Group
  name: system:unauthenticated
  apiGroup: rbac.authorization.k8s.io

For all users:

subjects:
- kind: Group
  name: system:authenticated
  apiGroup: rbac.authorization.k8s.io
- kind: Group
  name: system:unauthenticated
  apiGroup: rbac.authorization.k8s.io

Default roles and role bindings

API servers create a set of default ClusterRole and ClusterRoleBinding objects. Many of these are system: prefixed, which indicates that the resource is directly managed by the cluster control plane. All of the default ClusterRoles and ClusterRoleBindings are labeled with kubernetes.io/bootstrapping=rbac-defaults.

Auto-reconciliation

At each start-up, the API server updates default cluster roles with any missing permissions, and updates default cluster role bindings with any missing subjects. This allows the cluster to repair accidental modifications, and helps to keep roles and role bindings up-to-date as permissions and subjects change in new Kubernetes releases.

To opt out of this reconciliation, set the rbac.authorization.kubernetes.io/autoupdate annotation on a default cluster role or default cluster RoleBinding to false. Be aware that missing default permissions and subjects can result in non-functional clusters.

Auto-reconciliation is enabled by default if the RBAC authorizer is active.

API discovery roles

Default cluster role bindings authorize unauthenticated and authenticated users to read API information that is deemed safe to be publicly accessible (including CustomResourceDefinitions). To disable anonymous unauthenticated access, add --anonymous-auth=false flag to the API server configuration.

To view the configuration of these roles via kubectl run:

kubectl get clusterroles system:discovery -o yaml

User-facing roles

Some of the default ClusterRoles are not system: prefixed. These are intended to be user-facing roles. They include super-user roles (cluster-admin), roles intended to be granted cluster-wide using ClusterRoleBindings, and roles intended to be granted within particular namespaces using RoleBindings (admin, edit, view).

User-facing ClusterRoles use ClusterRole aggregation to allow admins to include rules for custom resources on these ClusterRoles. To add rules to the admin, edit, or view roles, create a ClusterRole with one or more of the following labels:

metadata:
  labels:
    rbac.authorization.k8s.io/aggregate-to-admin: "true"
    rbac.authorization.k8s.io/aggregate-to-edit: "true"
    rbac.authorization.k8s.io/aggregate-to-view: "true"