OIDC Authentication

The capsule-proxy works with kubectl users with a token-based authentication, e.g. OIDC or Bearer Token. In the following example, we'll use Keycloak as OIDC server capable to provides JWT tokens.

Configuring Keycloak

Configure Keycloak as OIDC server:

• Add a realm called caas, or use any existing realm instead
• Add a group capsule.clastix.io
• Add a user alice assigned to group capsule.clastix.io
• Add an OIDC client called kubernetes
• For the kubernetes client, create protocol mappers called groups and audience

If everything is done correctly, now you should be able to authenticate in Keycloak and see user groups in JWT tokens. Use the following snippet to authenticate in Keycloak as alice user:

$ KEYCLOAK=sso.clastix.io
$ REALM=caas
$ OIDC_ISSUER=${KEYCLOAK}/auth/realms/${REALM}

$ curl -k -s https://${OIDC_ISSUER}/protocol/openid-connect/token \
     -d grant_type=password \
     -d response_type=id_token \
     -d scope=openid \
     -d client_id=${OIDC_CLIENT_ID} \
     -d client_secret=${OIDC_CLIENT_SECRET} \
     -d username=${USERNAME} \
     -d password=${PASSWORD} | jq

The result will include an ACCESS_TOKEN, a REFRESH_TOKEN, and an ID_TOKEN. The access-token can generally be disregarded for Kubernetes. It would be used if the identity provider was managing roles and permissions for the users but that is done in Kubernetes itself with RBAC. The id-token is short lived while the refresh-token has longer expiration. The refresh-token is used to fetch a new id-token when the id-token expires.

{  
   "access_token":"ACCESS_TOKEN",
   "refresh_token":"REFRESH_TOKEN",
   "id_token": "ID_TOKEN",
   "token_type":"bearer",
   "scope": "openid groups profile email"
}

To introspect the ID_TOKEN token run:

$ curl -k -s https://${OIDC_ISSUER}/protocol/openid-connect/introspect \
     -d token=${ID_TOKEN} \
     --user ${OIDC_CLIENT_ID}:${OIDC_CLIENT_SECRET} | jq

The result will be like the following:

{
  "exp": 1601323086,
  "iat": 1601322186,
  "aud": "kubernetes",
  "typ": "ID",
  "azp": "kubernetes",
  "preferred_username": "alice",
  "email_verified": false,
  "acr": "1",
  "groups": [
    "capsule.clastix.io"
  ],
  "client_id": "kubernetes",
  "username": "alice",
  "active": true
}

Configuring Kubernetes API Server

Configuring Kubernetes for OIDC Authentication requires adding several parameters to the API Server. Please, refer to the documentation for details and examples. Most likely, your kube-apiserver.yaml manifest will looks like the following:

spec:
  containers:
  - command:
    - kube-apiserver
    ...
    - --oidc-issuer-url=https://${OIDC_ISSUER}
    - --oidc-ca-file=/etc/kubernetes/oidc/ca.crt
    - --oidc-client-id=${OIDC_CLIENT_SECRET}
    - --oidc-username-claim=preferred_username
    - --oidc-groups-claim=groups
    - --oidc-username-prefix=-

Configuring kubectl

There are two options to use kubectl with OIDC:

• OIDC Authenticator
• Use the --token option

To use the OIDC Authenticator, add an oidc user entry to your kubeconfig file:

$ kubectl config set-credentials oidc \
    --auth-provider=oidc \
    --auth-provider-arg=idp-issuer-url=https://${OIDC_ISSUER} \
    --auth-provider-arg=idp-certificate-authority=/path/to/ca.crt \
    --auth-provider-arg=client-id=${OIDC_CLIENT_ID} \
    --auth-provider-arg=client-secret=${OIDC_CLIENT_SECRET} \
    --auth-provider-arg=refresh-token=${REFRESH_TOKEN} \
    --auth-provider-arg=id-token=${ID_TOKEN} \
    --auth-provider-arg=extra-scopes=groups

To use the --token option:

$ kubectl config set-credentials oidc --token=${ID_TOKEN}

Point the kubectl to the URL where the capsule-proxy service is reachable:

$ kubectl config set-cluster mycluster \
    --server=https://kube.clastix.io \
    --certificate-authority=~/.kube/ca.crt

Create a new context for the OIDC authenticated users:

$ kubectl config set-context alice-oidc@mycluster \
    --cluster=mycluster \
    --user=oidc

As user alice, you should be able to use kubectl to create some namespaces:

$ kubectl --context alice-oidc@mycluster create namespace oil-production
$ kubectl --context alice-oidc@mycluster create namespace oil-development
$ kubectl --context alice-oidc@mycluster create namespace gas-marketing

and list only those namespaces:

$ kubectl --context alice-oidc@mycluster get namespaces
NAME                STATUS   AGE
gas-marketing       Active   2m
oil-development     Active   2m
oil-production      Active   2m

When logged as cluster-admin power user you should be able to see all namespaces:

$ kubectl get namespaces
NAME                STATUS   AGE
default             Active   78d
kube-node-lease     Active   78d
kube-public         Active   78d
kube-system         Active   78d
gas-marketing       Active   2m
oil-development     Active   2m
oil-production      Active   2m

Nota Bene: once your ID_TOKEN expires, the kubectl OIDC Authenticator will attempt to refresh automatically your ID_TOKEN using the REFRESH_TOKEN, the OIDC_CLIENT_ID and the OIDC_CLIENT_SECRET storing the new values for the REFRESH_TOKEN and ID_TOKEN in your kubeconfig file. In case the OIDC uses a self signed CA certificate, make sure to specify it with the idp-certificate-authority option in your kubeconfig file, otherwise you'll not able to refresh the tokens. Once the REFRESH_TOKEN is expired, you will need to refresh tokens manually.