Configuring clusters for Anthos Identity Service with OIDC

This document is for cluster administrators or application operators who want to configure Anthos Identity Service on individual clusters, allowing developers and other users to log in to the clusters using their existing identity details from an OpenID Connect (OIDC) provider. The guide assumes that you have read the Anthos Identity Service Overview.

• To find out how to set up Anthos Identity Service for a cluster with an LDAP provider instead, see Setting up Anthos Identity Service with LDAP.
• To find out how to set up Anthos Identity Service at fleet level for supported cluster types, with your authentication configuration managed by Google Cloud, see Setting up Anthos Identity Service for a fleet. This is a preview feature.

The instructions in this document assume that Anthos Identity Service has already been registered with your identity provider as a client application.

Setup overview

Setting up Anthos Identity Service for an individual cluster involves the following users and steps:

1. The platform administrator registers Anthos Identity Service as a client application with their preferred identity provider and gets a client ID and secret. To do this, follow the instructions in Configuring providers for Anthos Identity Service.
2. The cluster administrator configures clusters to use the service, following the instructions in this page.
3. The cluster administrator sets up user access, and optionally configures Kubernetes role-based access control (RBAC) for users on the clusters. To do this, follow the instructions in Setting up user access for Anthos Identity Service.

Prerequisites

• Your cluster must be an Anthos cluster on-premises (VMware or bare metal), on AWS, or on Azure. Per-cluster OIDC configuration is not supported for attached clusters or GKE clusters.
• To authenticate through the Cloud Console, each cluster that you want to configure for OIDC authentication must be registered to your project fleet.

Before you begin

• Ensure that your platform administrator has given you all the necessary information from Registering Anthos Identity Service with your provider before you start setup, including the client ID and secret for Anthos Identity Service.

• Ensure that you have the following command line tools installed:

  • The latest version of the Cloud SDK, which includes gcloud, the command line tool for interacting with Google Cloud. If you need to install the Cloud SDK, see the installation guide.
  • kubectl for running commands against Kubernetes clusters. If you need to install kubectl, see the installation guide

  If you are using Cloud Shell as your shell environment for interacting with Google Cloud, these tools are installed for you.

• Ensure that you have initialized the gcloud tool for use with the project where the clusters are registered.

• If you need to connect to an AWS or Azure Anthos cluster's control plane that is outside your current VPC through a bastion host, make sure that you have created the bastion host and started an SSH tunnel at port 8118 before this setup. Then prepend your kubectl commands when following this guide with HTTPS_PROXY=http://localhost:8118. If you used a different port when starting the SSH tunnel, replace 8118 with your selected port.

Configure clusters

To configure your clusters to use your chosen provider, Anthos Identity Service needs you to specify details about the identity provider, the information in the JWT tokens it provides for user identification, and other information provided when registering Anthos Identity Service as a client application.

So, for example, if your provider creates identity tokens with the following fields (among others), where iss is the identity provider URI, sub identifies the user, and groupList lists the security groups that the user belongs to:

{
  'iss': 'https://server.example.com'
  'sub': 'u98523-4509823'
  'groupList': ['[e-mail]', '[e-mail]']
  ...
}

...your configuration will have the following corresponding fields:

issuerURI: 'https://server.example.com'
userClaim: 'sub'
groupsClaim: 'groupList'
extraParams: 'resource=token-groups-claim'
...

(the extra parameter is required if you want to authorize access for groups)

Your platform adminstrator, or whoever manages identity in your organization, should provide you with most of the information you need to create the configuration.

Anthos Identity Service uses a Kubernetes custom resource type (CRD) called ClientConfig for cluster configuration, with fields for all the information Anthos Identity Service needs to interact with the identity provider. Each Anthos cluster has a ClientConfig resource named default in the kube-public namespace that you update with your configuration details, following the instructions below.

You can see some specific example configurations for popular providers in Provider-specific configurations.

kubectl

To edit your default ClientConfig, make sure you can connect to your cluster via kubectl, and run the following command:

kubectl --kubeconfig=KUBECONFIG_PATH edit ClientConfigs default -n kube-public

Replace KUBECONFIG_PATH with the path to your cluster's kubeconfig file—for example $HOME/.kube/config.

A text editor loads your cluster's ClientConfig resource. Add the spec.authentication.oidc object as shown below. Do not modify any default data that has already been written.

apiVersion: authentication.gke.io/v2alpha1
kind: ClientConfig
metadata:
  name: default
  namespace: kube-public
spec:
  authentication:
  - name: NAME
    oidc:
      certificateAuthorityData: CERTIFICATE_STRING
      clientID: CLIENT_ID
      clientSecret: CLIENT_SECRET
      deployCloudConsoleProxy: PROXY_BOOLEAN
      extraParams: EXTRA_PARAMS
      groupsClaim: GROUPS_CLAIM
      groupPrefix: GROUP_PREFIX
      issuerURI: ISSUER_URI
      kubectlRedirectURI: KUBECTL_REDIRECT_URI
      scopes: SCOPES
      userClaim: USER_CLAIM
      userPrefix: USER_PREFIX
      enableAccessToken: ENABLE_ACCESS_TOKEN
    proxy: PROXY_URL

The following table describes the fields of the ClientConfig oidc object. Most of the fields are optional. The fields you need to add depend on your identity provider and the setup options chosen by your platform admin when configuring the provider for Anthos Identity Service.

Field	Required	Description	Format
name	yes	The name you want to use to identify this configuration, typically the identity provider name. A configuration name must start with a letter followed by up to 39 lowercase letters, numbers, or hyphens, and cannot end with a hyphen.	String
certificateAuthorityData	No	If provided by your platform administrator, a PEM-encoded certificate string for the identity provider. Include the resulting string in certificateAuthorityData as a single line.	String
clientID	Yes	The client ID returned when registering Anthos Identity Service with your provider.	String
clientSecret	No	Shared secret between the OIDC client application and the OIDC provider.	String
deployCloudConsoleProxy	No	Specifies whether a proxy is deployed that lets the Cloud Console connect to an on-premises identity provider that is not publicly accessible over the internet. By default this is set to false.	Boolean
extraParams	No	Additional key=value parameters to send to the identity provider, specified as a comma-separated list—for example `prompt=consent,access_type=offline`.	Comma-delimited list
groupsClaim	No	The JWT claim (field name) that your provider uses to return an account's security groups.	String
groupPrefix	No	The prefix you want to prepend to security group names to avoid clashes with existing names in your access control rules if you have configurations for multiple identity providers (typically the provider name).	String
issuerURI	Yes	The URI where authorization requests are made to your identity provider. The URI must use HTTPS.	URL String
kubectlRedirectURI	Yes	The redirect URL and port used by the Cloud SDK and specified by your platform admin at registration, typically in the form `http://localhost:PORT/callback`.	URL String
scopes	Yes	Additional scopes to send to the OpenID provider. For example, Microsoft Azure and Okta require the offline_access scope.	Comma-delimited list
userClaim	No	The JWT claim (field name) that your provider uses to identify a user account. If you don't specify a value here, Anthos Identity Service uses "sub", which is the user ID claim used by many providers. You can choose other claims, such as "email" or "name", depending on the OpenID provider. Claims other than "email" are prefixed with the issuer URL to prevent naming clashes.	String
userPrefix	No	The prefix you want prepended to user claims to prevent clashes with existing names, if you don't want to use the default prefix.	String
enableAccessToken	No	If enabled, Anthos Identity Service can use the identity provider's userinfo endpoint to get groups information when a user logs in from the command line. This lets you use security groups for authorization if you have a provider (such as Okta) that provides group claims from this endpoint. If not set, this is considered to be false.	Boolean
proxy	No	Proxy server address to use to connect to the identity provider, if applicable. You might need to set this if, for example, your cluster is in a private network and needs to connect to a public identity provider. For example: http://user:password@10.10.10.10:8888.	String

After you complete your ClientConfig, save the file, which updates the ClientConfig on your cluster. If you make any syntax errors, you are prompted to re-edit the config to fix them.

Provider-specific configurations

This section provides configuration guidance for some popular OIDC providers, including example configurations that you can copy and edit with your own details.

Azure AD

...
spec:
  authentication:
  - name: oidc-ad
    oidc:
      clientID: CLIENT_ID
      clientSecret: CLIENT_SECRET
      cloudConsoleRedirectURI: https://console.cloud.google.com/kubernetes/oidc
      extraParams: prompt=consent, access_type=offline
      issuerURI: https://login.microsoftonline.com/TENANT_ID/v2.0
      kubectlRedirectURI: http://localhost:PORT/callback
      scopes: openid,email,offline_access
      userClaim: email
...

Getting group information with azuread (on-premises clusters only)

Preview

This product or feature is covered by the Pre-GA Offerings Terms of the Google Cloud Terms of Service. Pre-GA products and features might have limited support, and changes to pre-GA products and features might not be compatible with other pre-GA versions. For more information, see the launch stage descriptions.

From Anthos 1.9, Anthos Identity Service lets you configure on-premises Anthos clusters (both VMware and bare metal) for Azure AD by adding a specific azuread section in your ClientConfig instead of oidc. Using this configuration lets Anthos Identity Service get users' group membership information from Azure AD, even if the user is a member of more than 200 groups (Azure AD can only provide up to approximately 200 groups per user with our default OIDC configuration). This lets you set up Kubernetes role based access control (RBAC) based on groups.

• Your platform admin must have set up Anthos Identity Service as a client with the relevant permissions to use this feature.
• Each user must have an associated email address configured as their identifier in Azure AD. Anthos Identity Service uses the user's email to assert the user's identity and authenticate the request.

If you don't need to use group membership information, you can still use an azuread section instead of oidc to simplify configuration of on-premises clusters for Azure AD: defaults for any remaining configuration information are provided by Anthos Identity Service.

Add an azuread section as follows. All fields are required.

...
spec:
  authentication:
  - name: NAME
    azureAD:
      clientID: CLIENT_ID
      clientSecret: CLIENT_SECRET
      tenant: TENANT_ID
      kubectlRedirectURI: http://localhost:PORT/callback
...

Replace the following:

• NAME: The name you want to use to identify this configuration, typically the identity provider name. A configuration name must start with a letter followed by up to 39 lowercase letters, numbers, or hyphens, and cannot end with a hyphen.
• CLIENT_ID: The client ID returned when registering Anthos Identity Service with your provider.
• CLIENT_SECRET: Shared secret between the OIDC client application and the OIDC provider.
• TENANT: The kind of Azure AD account to be authenticated. Supported values are the tenant ID, or the tenant name for accounts belonging to a specific tenant. The tenant name is also known as the primary domain. For details on how to find these values, see Find the Microsoft Azure AD tenant ID and primary domain name.
• PORT: The port number chosen for the redirect URL used by the Cloud SDK, specified by your platform admin at registration.

Okta

With this config, you can authenticate using both users and groups with Okta as the identity provider.

...
spec:
  authentication:
  - name: okta
    oidc:
      clientID: CLIENT_ID
      clientSecret: CLIENT_SECRET
      cloudConsoleRedirectURI: https://console.cloud.google.com/kubernetes/oidc
      enableAccessToken: true
      extraParams: prompt=consent
      groupsClaim: groups
      issuerURI: https://OKTA_ISSUER_URI/
      kubectlRedirectURI: http://localhost:PORT/callback
      scopes: offline_access,email,profile,groups
      userClaim: email
...

What's next?

After the configuration is applied, continue to set up user access to clusters.