Authentik Oidc Kubernetes

Authentik OIDC for Kubernetes API Authentication

Problem

Setting up Authentik as an OIDC identity provider for Kubernetes kubectl access involves multiple non-obvious pitfalls that cause silent failures at different stages of the authentication flow.

Context / Trigger Conditions

• Setting up multi-user kubectl access with OIDC
• Using Authentik as the identity provider and kubelogin (int128/kubelogin) as the kubectl plugin
• Any of these errors:
  • oidc: email not verified
  • oidc: parse username claims "email": claim not present
  • The request fails due to a missing, invalid, or mismatching redirection URI
  • JWKS endpoint (/application/o/<app>/jwks/) returns {}
  • Unauthorized after successful browser login

Solution

Gotcha 1: Signing Key Must Be Assigned

Authentik's OAuth2 provider does NOT assign a signing key by default. Without it, the JWKS endpoint returns {} and kube-apiserver can't validate tokens.

Fix: Assign a signing key (e.g., "authentik Self-signed Certificate") to the OAuth2 provider:

# Via Django shell (kubectl exec into authentik server pod)
from authentik.providers.oauth2.models import OAuth2Provider
from authentik.crypto.models import CertificateKeyPair

provider = OAuth2Provider.objects.get(name='kubernetes')
cert = CertificateKeyPair.objects.filter(name='authentik Self-signed Certificate').first()
provider.signing_key = cert
provider.save()

Or via API:

curl -X PATCH -H "Authorization: Bearer $TOKEN" -H "Content-Type: application/json" \
  "$AUTHENTIK_URL/api/v3/providers/oauth2/<pk>/" \
  -d '{"signing_key": "<certificate-keypair-uuid>"}'

Gotcha 2: Default Email Mapping Sets email_verified: False

Authentik's built-in email scope mapping hardcodes email_verified: False:

return {
    "email": request.user.email,
    "email_verified": False  # <-- This causes kube-apiserver to reject the token
}

kube-apiserver requires email_verified: true by default.

Fix: Create a custom scope mapping with email_verified: True and assign it to the provider instead of the default:

from authentik.providers.oauth2.models import OAuth2Provider, ScopeMapping

# Create custom mapping
mapping, _ = ScopeMapping.objects.get_or_create(
    name='Kubernetes Email (verified)',
    defaults={
        'scope_name': 'email',
        'expression': 'return {"email": request.user.email, "email_verified": True}'
    }
)

# Replace default email mapping on the provider
provider = OAuth2Provider.objects.get(name='kubernetes')
default_email = ScopeMapping.objects.filter(
    managed='goauthentik.io/providers/oauth2/scope-email'
).first()
if default_email:
    provider.property_mappings.remove(default_email)
provider.property_mappings.add(mapping)

Gotcha 3: kubelogin Needs Extra Scopes

By default, kubelogin only requests the openid scope. The token will lack email and groups claims, causing:

oidc: parse username claims "email": claim not present

Fix: Add --oidc-extra-scope flags to the kubeconfig exec plugin:

users:
- name: oidc-user
  user:
    exec:
      command: kubectl
      args:
        - oidc-login
        - get-token
        - --oidc-issuer-url=https://authentik.example.com/application/o/kubernetes/
        - --oidc-client-id=kubernetes
        - --oidc-extra-scope=email      # Required!
        - --oidc-extra-scope=profile
        - --oidc-extra-scope=groups

Gotcha 4: Redirect URIs Must Use Regex Mode

kubelogin picks a random available port (tries 8000, 18000, then random). Strict redirect URI matching like http://localhost:8000/callback will fail when kubelogin uses a different port.

Fix: Use regex matching in the Authentik provider:

{
  "redirect_uris": [
    {"matching_mode": "regex", "url": "http://localhost:.*"},
    {"matching_mode": "regex", "url": "http://127\\.0\\.0\\.1:.*"}
  ]
}

Gotcha 5: Property Mappings API Endpoint Changed

In Authentik 2025.10.x, scope mappings are at:

• propertymappings/provider/scope/ (new, correct)
• NOT propertymappings/scope/ (old, returns 405 Method Not Allowed on POST)

Gotcha 6: Static Pod Manifest Changes Need Full Cycle

See skill: kubelet-static-pod-manifest-update for the full restart procedure.

Verification

After all fixes:

# 1. JWKS has a key
curl -s https://authentik.example.com/application/o/kubernetes/jwks/ | jq '.keys | length'
# Expected: 1 (or more)

# 2. Test auth
KUBECONFIG=/path/to/oidc-kubeconfig kubectl get namespaces
# Expected: browser opens, login, namespaces returned

# 3. Check API server logs for success
ssh master "sudo kubectl logs -n kube-system kube-apiserver-* | grep oidc | tail -5"
# Expected: no "Unable to authenticate" errors

Notes

• The OAuth2 provider should use client_type: public (no client secret needed for kubelogin)
• Set sub_mode: user_email so the OIDC subject matches the RBAC binding
• Set include_claims_in_id_token: true for the token to contain claims directly
• Use issuer_mode: per_provider for a clean issuer URL
• RBAC ClusterRoleBindings should match on the user's email (the --oidc-username-claim=email value)