Put the artifactapi web UI behind Authentik oauth2-proxy (#456)

The artifactapi web UI is open to anyone who can reach the host. Front it with Authentik SSO gated on akP-artifactapi-admin, while leaving the package-manager surfaces (/api/v1, /api/v2, /v2 docker registry, /terraform, /.well-known) untouched — dnf, containerd mirrors, buildah, terraform and CI publish steps cannot do a browser flow.

- Add the oauth2-proxy ConfigMap, Deployment, Service and VMPodScrape.
- Add the oauth-credentials VaultStaticSecret.
- Point the api-route /ui rule at oauth2-proxy and add a /oauth2 rule; the catch-all / rule still goes straight to the api Service on both listeners.

Requires terraform-authentik #34 applied and the Vault kv seed first.

Reviewed-on: #456
Co-authored-by: unkin-agent <unkin-agent@unkin.net>
Co-committed-by: unkin-agent <unkin-agent@unkin.net>

apps/base/artifactapi/httproute.yaml

@@ -1,4 +1,21 @@
 ---
+# Path split between the authenticated UI and the unauthenticated machine API.
+# Longest matching prefix wins, so the two UI rules take precedence over "/".
+#
+# AUTHENTICATED (oauth2 Service -> oauth2-proxy -> ui Service):
+#   /oauth2   oauth2-proxy sign_in / start / callback / sign_out
+#   /ui       the human-facing SPA
+#
+# NOT AUTHENTICATED (artifactapi Service, unchanged):
+#   /api/v1/{remote,local,virtual}/*   package proxy reads (yum/dnf, pip, ...)
+#   /api/v2/remotes|virtuals|locals/*  management API + the UI's own XHR calls
+#   /api/v2/remotes/{name}/files/*     CI publish uploads (PUT) and downloads
+#   /v2/*                              Docker Registry V2 (containerd, buildah)
+#   /terraform/v1/providers/*          Terraform provider registry
+#   /.well-known/terraform.json        Terraform service discovery
+#   /health, /version, /               probes and the redirect to /ui/
+# Those clients cannot complete a browser OIDC flow, so they must never be
+# routed through oauth2-proxy.
 apiVersion: gateway.networking.k8s.io/v1
 kind: HTTPRoute
 metadata:
@@ -22,7 +39,17 @@ spec:
     - backendRefs:
         - group: ""
           kind: Service
-          name: ui
+          name: oauth2
+          port: 80
+          weight: 1
+      matches:
+        - path:
+            type: PathPrefix
+            value: /oauth2
+    - backendRefs:
+        - group: ""
+          kind: Service
+          name: oauth2
           port: 80
           weight: 1
       matches: