Kubernetes with OIDC authentication

How does it work?

See kubernetes.io - Authentication

The K8S API server can be configured to support OIDC authentication based on JWT tokens by adding some parameters:

# the OIDC issuer URL
--kube-apiserver-arg oidc-issuer-url=https://keycloak.quadtreeworld.net/realms/master
--kube-apiserver-arg oidc-client-id=kubernetes
--kube-apiserver-arg oidc-groups-claim=groups
--kube-apiserver-arg oidc-groups-prefix=oidc:
--kube-apiserver-arg oidc-username-claim=email
--kube-apiserver-arg oidc-username-prefix=oidc:

Note that :

• Prefixes avoid conflicts with K8S groups
• The oidc-client-id is used by K8S to control the audience of the token (“aud”). So, if you use a dedicated “headlamp” client, make sure that “kubernetes” is added (see Add audience mapper with Keycloak)

Using OIDC with devbox

Note that:

• docker-devbox - kind allows to create a Kind cluster with OIDC support.
• mborne/k3s-deploy does the same with a K3S cluster (see mborne/k3s-deploy - Enabling OIDC on K3S)
• OVH - Managed Kubernetes Service allows OIDC configuration (see help.ovhcloud.com - Configuring the OIDC provider on an OVHcloud Managed Kubernetes cluster)
• Other providers like Google Kubernetes Engine (GKE) provide an equivalent feature by binding users and groups from their IAMs.

RBAC configuration with OIDC

See kubernetes.io - Using RBAC Authorization

You can assign a Role or ClusterRole to users and groups. See the following examples:

# Grant "cluster-admin" role to an OIDC user :
kubectl create clusterrolebinding oidc-mborne-admin --clusterrole=cluster-admin --user='oidc:mborne@quadtreeworld.net'

# Grant "cluster-admin" role to the member of an OIDC group :
kubectl create clusterrolebinding oidc-devbox-admins --clusterrole=cluster-admin --group='oidc:devbox_admins'

# DANGEROUS: Grant "view" role to all authenticated users
kubectl create clusterrolebinding everybody-can-view-everything  --clusterrole=view --group='system:authenticated'

RBAC debugging

See kubernetes.io - kubectl auth can-i

# check permissions at K8S level
kubectl auth can-i list pods --as=system:authenticated
kubectl auth can-i list pods --as=oidc:mborne@example.net
kubectl auth can-i list pods --as=mborne@example.net

Resources

Add audience mapper with Keycloak

See Client / Mappers / Add mapper (by configuration) / Audience, then :

• Select “kubernetes” kubernetes
• Check “Add to ID token”

Show screenshot