authelia: Set up OIDC for k8s API server

Enabling OpenID Connect authentication for the Kubernetes API server
will allow clients, particularly `kubectl` to log in without needing
TLS certificates and private keys.

authelia/configuration.yml

@@ -29,6 +29,13 @@ identity_providers:
       - email
       - offline_access
       authorization_policy: one_factor
+    - id: kubernetes
+      description: Kubernetes
+      public: true
+      redirect_uris:
+      - http://localhost:8000
+      - http://localhost:18000
+      authorization_policy: one_factor
 
 log:
   level: trace