Grant users access to Kubernetes with an external OIDC provider

Amazon EKS supports using OpenID Connect (OIDC) identity providers as a method to authenticate users to your cluster. OIDC identity providers can be used with, or as an alternative to AWS Identity and Access Management (IAM). For more information about using IAM, see Grant IAM users and roles access to Kubernetes APIs. After configuring authentication to your cluster, you can create Kubernetes roles and clusterroles to assign permissions to the roles, and then bind the roles to the identities using Kubernetes rolebindings and clusterrolebindings. For more information, see Using RBAC Authorization in the Kubernetes documentation.

• You can associate one OIDC identity provider to your cluster.

• Kubernetes doesn’t provide an OIDC identity provider. You can use an existing public OIDC identity provider, or you can run your own identity provider. For a list of certified providers, see OpenID Certification on the OpenID site.

• The issuer URL of the OIDC identity provider must be publicly accessible, so that Amazon EKS can discover the signing keys. Amazon EKS doesn’t support OIDC identity providers with self-signed certificates.

• You can’t disable IAM authentication to your cluster, because it’s still required for joining nodes to a cluster.

• An Amazon EKS cluster must still be created by an AWS IAM principal, rather than an OIDC identity provider user. This is because the cluster creator interacts with the Amazon EKS APIs, rather than the Kubernetes APIs.

• OIDC identity provider-authenticated users are listed in the cluster’s audit log if CloudWatch logs are turned on for the control plane. For more information, see Enable or disable control plane logs.

• You can’t sign in to the AWS Management Console with an account from an OIDC provider. You can only View Kubernetes resources in the AWS Management Console by signing into the AWS Management Console with an AWS Identity and Access Management account.

Associate an OIDC identity provider

Before you can associate an OIDC identity provider with your cluster, you need the following information from your provider:

Issuer URL

The URL of the OIDC identity provider that allows the API server to discover public signing keys for verifying tokens. The URL must begin with https:// and should correspond to the iss claim in the provider’s OIDC ID tokens. In accordance with the OIDC standard, path components are allowed but query parameters are not. Typically the URL consists of only a host name, like https://server.example.org or https://example.com . This URL should point to the level below .well-known/openid-configuration and must be publicly accessible over the internet.

Client ID (also known as audience)

The ID for the client application that makes authentication requests to the OIDC identity provider.

You can associate an identity provider using eksctl or the AWS Management Console.

Associate an identity provider using eksctl

1. Create a file named associate-identity-provider.yaml with the following contents. Replace the example values with your own. The values in the identityProviders section are obtained from your OIDC identity provider. Values are only required for the name, type, issuerUrl, and clientId settings under identityProviders.

   ---
   apiVersion: eksctl.io/v1alpha5
   kind: ClusterConfig
   
   metadata:
     name: my-cluster
     region: your-region-code
   
   identityProviders:
     - name: my-provider
       type: oidc
       issuerUrl: https://example.com
       clientId: kubernetes
       usernameClaim: email
       usernamePrefix: my-username-prefix
       groupsClaim: my-claim
       groupsPrefix: my-groups-prefix
       requiredClaims:
         string: string
       tags:
         env: dev

   Important

   Don’t specify system:, or any portion of that string, for groupsPrefix or usernamePrefix.

2. Create the provider.

   eksctl associate identityprovider -f associate-identity-provider.yaml

3. To use kubectl to work with your cluster and OIDC identity provider, see Using kubectl in the Kubernetes documentation.

Associate an identity provider using the AWS Console

1. Open the Amazon EKS console.

2. Select your cluster, and then select the Access tab.

3. In the OIDC Identity Providers section, select* Associate Identity Provider*.

4. On the Associate OIDC Identity Provider page, enter or select the following options, and then select Associate.

   • For Name, enter a unique name for the provider.

   • For Issuer URL, enter the URL for your provider. This URL must be accessible over the internet.

   • For Client ID, enter the OIDC identity provider’s client ID (also known as audience).

   • For Username claim, enter the claim to use as the username.

   • For Groups claim, enter the claim to use as the user’s group.

   • (Optional) Select Advanced options, enter or select the following information.

     • Username prefix – Enter a prefix to prepend to username claims. The prefix is prepended to username claims to prevent clashes with existing names. If you do not provide a value, and the username is a value other than email, the prefix defaults to the value for Issuer URL. You can use the value - to disable all prefixing. Don’t specify system: or any portion of that string.

     • Groups prefix – Enter a prefix to prepend to groups claims. The prefix is prepended to group claims to prevent clashes with existing names (such as system: groups). For example, the value oidc: creates group names like oidc:engineering and oidc:infra. Don’t specify system: or any portion of that string..

     • Required claims – Select Add claim and enter one or more key value pairs that describe required claims in the client ID token. The pairs describe required claims in the ID Token. If set, each claim is verified to be present in the ID token with a matching value.

       1. To use kubectl to work with your cluster and OIDC identity provider, see Using kubectl in the Kubernetes documentation.

Example IAM policy

If you want to prevent an OIDC identity provider from being associated with a cluster, create and associate the following IAM policy to the IAM accounts of your Amazon EKS administrators. For more information, see Creating IAM policies and Adding IAM identity permissions in the IAM User Guide and Actions in the Service Authorization Reference.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "denyOIDC",
            "Effect": "Deny",
            "Action": [
                "eks:AssociateIdentityProviderConfig"
            ],
            "Resource": "arn:aws:eks:us-west-2.amazonaws.com:111122223333:cluster/*"

        },
        {
            "Sid": "eksAdmin",
            "Effect": "Allow",
            "Action": [
                "eks:*"
            ],
            "Resource": "*"
        }
    ]
}

The following example policy allows OIDC identity provider association if the clientID is kubernetes and the issuerUrl is https://cognito-idp.us-west-2amazonaws.com/* .

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "AllowCognitoOnly",
            "Effect": "Deny",
            "Action": "eks:AssociateIdentityProviderConfig",
            "Resource": "arn:aws:eks:us-west-2:111122223333:cluster/my-instance",
            "Condition": {
                "StringNotLikeIfExists": {
                    "eks:issuerUrl": "https://cognito-idp.us-west-2.amazonaws.com/*"
                }
            }
        },
        {
            "Sid": "DenyOtherClients",
            "Effect": "Deny",
            "Action": "eks:AssociateIdentityProviderConfig",
            "Resource": "arn:aws:eks:us-west-2:111122223333:cluster/my-instance",
            "Condition": {
                "StringNotEquals": {
                    "eks:clientId": "kubernetes"
                }
            }
        },
        {
            "Sid": "AllowOthers",
            "Effect": "Allow",
            "Action": "eks:*",
            "Resource": "*"
        }
    ]
}