Wire ArgoCD to Authentik OIDC (#253)

## Why

ArgoCD had no external ingress and only local admin auth. This exposes `argocd-server` behind the traefik-internal gateway and enables Authentik SSO, so operators log in with their Authentik identity and group membership. Pairs with unkin/terraform-authentik#3 (creates the OAuth2 provider).

## Changes

- **argocd-cm**: set `url` and `oidc.config` (Authentik issuer `identity.unkin.net/application/o/argocd/`, `argocd` client, openid/profile/email scopes). Client secret resolved from the `argocd-oidc` Secret via `$argocd-oidc:client_secret`.
- **argocd-rbac-cm**: match RBAC on the `groups` claim; default `role:readonly`; map the `argocd-admins` Authentik group to `role:admin`.
- **argocd-cmd-params-cm**: `server.insecure=true` so `argocd-server` serves HTTP behind the TLS-terminating gateway.
- Add **Gateway + HTTPRoutes** for `argocd.k8s.syd1.au.unkin.net` (mirrors the grafana pattern: traefik-internal, vault-issuer cert, external-dns).
- Add **VaultAuth + VaultStaticSecret** sourcing the OIDC client secret from `kv/kubernetes/namespace/argocd/default/oauth-credentials` into the `argocd-oidc` Secret (labelled `part-of=argocd` so ArgoCD will resolve the `$` reference).

## Notes / rollout

- Seed the client secret in Vault out of band (same path terraform-authentik reads).
- The argocd namespace `default` SA already has Vault read access via the `default` k8s role, so no terraform-vault change is needed.
- `argocd-server` needs a one-time rollout restart to pick up `server.insecure`.

Validated with `kustomize build --enable-helm clusters/au-syd1/bootstrap`, `make kubeconform`, and pre-commit (yamllint + no-plain-secrets).

Reviewed-on: #253
Co-authored-by: Ben Vincent <ben@unkin.net>
Co-committed-by: Ben Vincent <ben@unkin.net>

clusters/au-syd1/bootstrap/argocd-cm-patch.yaml

@@ -6,3 +6,20 @@ metadata:
   namespace: argocd
 data:
   kustomize.buildOptions: "--enable-helm"
+  # External URL ArgoCD serves on (TLS terminated at the traefik-internal gateway).
+  url: https://argocd.k8s.syd1.au.unkin.net
+  # OIDC login via Authentik. The client secret is seeded in Vault out of band
+  # and surfaced as the `argocd-oidc` Secret (labelled part-of=argocd) by VSO;
+  # `$argocd-oidc:client_secret` resolves the key from that Secret.
+  oidc.config: |
+    name: Authentik
+    issuer: https://identity.unkin.net/application/o/argocd/
+    clientID: argocd
+    clientSecret: $argocd-oidc:client_secret
+    requestedScopes:
+      - openid
+      - profile
+      - email
+    requestedIDTokenClaims:
+      groups:
+        essential: true

clusters/au-syd1/bootstrap/argocd-cmd-params-cm-patch.yaml

@@ -0,0 +1,10 @@
+---
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: argocd-cmd-params-cm
+  namespace: argocd
+data:
+  # argocd-server serves plain HTTP; TLS is terminated at the traefik-internal
+  # gateway in front of it. Required so the gateway can route to port 80.
+  server.insecure: "true"

clusters/au-syd1/bootstrap/argocd-oidc-vaultauth.yaml

@@ -0,0 +1,18 @@
+---
+apiVersion: secrets.hashicorp.com/v1beta1
+kind: VaultAuth
+metadata:
+  name: default
+  namespace: argocd
+spec:
+  method: kubernetes
+  mount: k8s/au/syd1
+  vaultConnectionRef: vso-system/default
+  allowedNamespaces:
+    - argocd
+  kubernetes:
+    role: default
+    serviceAccount: default
+    audiences:
+      - vault
+    tokenExpirationSeconds: 600

clusters/au-syd1/bootstrap/argocd-oidc-vaultstaticsecret.yaml

@@ -0,0 +1,23 @@
+---
+apiVersion: secrets.hashicorp.com/v1beta1
+kind: VaultStaticSecret
+metadata:
+  name: argocd-oidc
+  namespace: argocd
+spec:
+  vaultAuthRef: default
+  mount: kv
+  type: kv-v2
+  # Seeded out of band; same secret is read by terraform-authentik to configure
+  # the provider's client_secret. Key: client_secret.
+  path: kubernetes/namespace/argocd/default/oauth-credentials
+  refreshAfter: 5m
+  hmacSecretData: true
+  destination:
+    name: argocd-oidc
+    create: true
+    overwrite: true
+    # ArgoCD only resolves `$secret:key` references against Secrets carrying
+    # this label.
+    labels:
+      app.kubernetes.io/part-of: argocd

clusters/au-syd1/bootstrap/argocd-rbac-cm-patch.yaml

@@ -0,0 +1,14 @@
+---
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: argocd-rbac-cm
+  namespace: argocd
+data:
+  # Match RBAC subjects against the `groups` claim from Authentik.
+  scopes: "[groups]"
+  # Authenticated users with no matching group get read-only access.
+  policy.default: role:readonly
+  # Authentik group -> ArgoCD role.
+  policy.csv: |
+    g, argocd-admins, role:admin

clusters/au-syd1/bootstrap/argocd-server-gateway.yaml

@@ -0,0 +1,39 @@
+---
+apiVersion: gateway.networking.k8s.io/v1
+kind: Gateway
+metadata:
+  name: argocd-server
+  namespace: argocd
+  labels:
+    app.kubernetes.io/name: argocd-server
+    app.kubernetes.io/instance: argocd
+    traefik.io/instance: internal
+  annotations:
+    cert-manager.io/cluster-issuer: vault-issuer
+    cert-manager.io/common-name: argocd.k8s.syd1.au.unkin.net
+    cert-manager.io/private-key-size: "4096"
+    external-dns.alpha.kubernetes.io/hostname: argocd.k8s.syd1.au.unkin.net
+    external-dns.alpha.kubernetes.io/target: 198.18.200.4
+spec:
+  gatewayClassName: traefik-internal
+  listeners:
+    - name: http
+      port: 80
+      protocol: HTTP
+      hostname: argocd.k8s.syd1.au.unkin.net
+      allowedRoutes:
+        namespaces:
+          from: Same
+    - name: https
+      port: 443
+      protocol: HTTPS
+      hostname: argocd.k8s.syd1.au.unkin.net
+      allowedRoutes:
+        namespaces:
+          from: Same
+      tls:
+        mode: Terminate
+        certificateRefs:
+          - group: ""
+            kind: Secret
+            name: argocd-server-tls

clusters/au-syd1/bootstrap/argocd-server-httproute.yaml

@@ -0,0 +1,55 @@
+---
+apiVersion: gateway.networking.k8s.io/v1
+kind: HTTPRoute
+metadata:
+  name: argocd-server-http-redirect
+  namespace: argocd
+  labels:
+    app.kubernetes.io/name: argocd-server
+    app.kubernetes.io/instance: argocd
+spec:
+  hostnames:
+    - argocd.k8s.syd1.au.unkin.net
+  parentRefs:
+    - group: gateway.networking.k8s.io
+      kind: Gateway
+      name: argocd-server
+      sectionName: http
+  rules:
+    - filters:
+        - type: RequestRedirect
+          requestRedirect:
+            scheme: https
+            statusCode: 301
+      matches:
+        - path:
+            type: PathPrefix
+            value: /
+---
+apiVersion: gateway.networking.k8s.io/v1
+kind: HTTPRoute
+metadata:
+  name: argocd-server
+  namespace: argocd
+  labels:
+    app.kubernetes.io/name: argocd-server
+    app.kubernetes.io/instance: argocd
+spec:
+  hostnames:
+    - argocd.k8s.syd1.au.unkin.net
+  parentRefs:
+    - group: gateway.networking.k8s.io
+      kind: Gateway
+      name: argocd-server
+      sectionName: https
+  rules:
+    - backendRefs:
+        - group: ""
+          kind: Service
+          name: argocd-server
+          port: 80
+          weight: 1
+      matches:
+        - path:
+            type: PathPrefix
+            value: /

clusters/au-syd1/bootstrap/kustomization.yaml

@@ -7,12 +7,25 @@ resources:
   - https://artifactapi.k8s.syd1.au.unkin.net/api/v1/remote/github/kubernetes-sigs/gateway-api/releases/download/v1.5.1/standard-install.yaml
   - au-syd1-apps.yaml
   - argocd-self-app.yaml
+  # Authentik OIDC: expose argocd-server and wire the client secret from Vault.
+  - argocd-server-gateway.yaml
+  - argocd-server-httproute.yaml
+  - argocd-oidc-vaultauth.yaml
+  - argocd-oidc-vaultstaticsecret.yaml
 
 patches:
   - path: argocd-cm-patch.yaml
     target:
       kind: ConfigMap
       name: argocd-cm
+  - path: argocd-rbac-cm-patch.yaml
+    target:
+      kind: ConfigMap
+      name: argocd-rbac-cm
+  - path: argocd-cmd-params-cm-patch.yaml
+    target:
+      kind: ConfigMap
+      name: argocd-cmd-params-cm
   - path: argocd-tls-certs-patch.yaml
     target:
       kind: ConfigMap