fix(headlamp): per-environment OIDC URLs — prod was dialing DEV's Keycloak

The operator could not log in to Headlamp on prod:

  Get "https://keycloak.home.keithjackson.dev/realms/homelab/.well-known/openid-configuration":
  dial tcp 192.168.1.53:443: i/o timeout

ROOT CAUSE: OIDC_ISSUER_URL and OIDC_CALLBACK_URL were keys INSIDE the SOPS-encrypted
headlamp-oidc-credentials.sops.yaml. Flux's ${BASE_DOMAIN} postBuild substitution rewrites
the RENDERED manifest text and can never reach inside ciphertext, so both values were frozen
at the apex `home.keithjackson.dev` in BOTH environments. Dev IS the apex, so dev looked
correct; prod (BASE_DOMAIN = prod.home.keithjackson.dev) therefore pointed at dev's Keycloak
at 192.168.1.53 — on the dev LAN behind pfSense, unroutable from prod's 192.168.2.0/24.

FIX: an issuer URL and a callback URL are PUBLIC. Move both out of the Secret into the
HelmRelease's spec.values.env, written with ${BASE_DOMAIN} so substitution resolves them per
environment. The Secret keeps only what is genuinely secret or environment-invariant
(OIDC_CLIENT_SECRET, OIDC_CLIENT_ID, OIDC_SCOPES).

Exactly ONE source per variable: the chart renders `env:` after `envFrom:`, and an explicit
env entry silently WINS over the same name from envFrom — so the two sets must not overlap,
and they no longer do. The five load-bearing names the chart's $(...) args require
(OIDC_CLIENT_ID/CLIENT_SECRET/ISSUER_URL/SCOPES/CALLBACK_URL) are all still delivered;
verified by rendering platform/headlamp per overlay, `flux envsubst --strict`, and
`helm template` of chart 0.41.0 against the substituted values.

Side effect, deliberate: naming OIDC_CALLBACK_URL in `env:` makes the chart finally EMIT
`-oidc-callback-url=$(OIDC_CALLBACK_URL)` — it gates that arg on the value being set via
`env:`/`config.oidc`, which a Secret key alone never tripped, so the Secret's callback URL
had been dead weight. The value is byte-identical to the single redirectUri registered on the
Keycloak `headlamp` client (also ${BASE_DOMAIN}-templated), the only URI Keycloak accepts.

[parity] holds: prod's kube-apiserver oidc-issuer-url is an install-time k3s flag from
k3s_base_domain=prod.home.keithjackson.dev, which is exactly what Headlamp now uses.

Co-Authored-By: Claude Opus 5 <[email protected]>

platform/headlamp/README.md

@@ -1,6 +1,6 @@
 # Headlamp — Kubernetes dashboard (Keycloak OIDC + per-user RBAC)
 
-Headlamp is served at `https://headlamp.home.keithjackson.dev` behind the shared Gateway
+Headlamp is served at `https://headlamp.${BASE_DOMAIN}` behind the shared Gateway
 (wildcard TLS), with **native Keycloak OIDC login** and **per-user RBAC** (ADR-0014, docs/15).
 
 ## How per-user RBAC works (end to end)
@@ -33,6 +33,49 @@ carry `aud=[headlamp, kubernetes]`:
 
 This keeps the apiserver OIDC config untouched (preferred over widening `--api-audiences`).
 
+## Where the OIDC config comes from (two sources, no overlap)
+
+The container needs five env vars, and their **names are load-bearing**: the chart's args reference
+them via `$(...)` (`-oidc-idp-issuer-url=$(OIDC_ISSUER_URL)`, `-oidc-client-id=$(OIDC_CLIENT_ID)`, …).
+They must be exactly `OIDC_CLIENT_ID`, `OIDC_CLIENT_SECRET`, `OIDC_ISSUER_URL`, `OIDC_SCOPES`,
+`OIDC_CALLBACK_URL` — **not** camelCase. A misnamed or missing name does **not** fail loudly:
+Kubernetes leaves the literal string `$(OIDC_ISSUER_URL)` in the argument and login dies with
+`unsupported protocol scheme ""`.
+
+| Env var | Source | Why |
+|---|---|---|
+| `OIDC_CLIENT_ID`, `OIDC_SCOPES`, `OIDC_CLIENT_SECRET` | `headlamp-oidc-credentials.sops.yaml`, `envFrom`'d by `config.oidc.externalSecret` | secret, or environment-invariant |
+| `OIDC_ISSUER_URL`, `OIDC_CALLBACK_URL` | `helmrelease.yaml` → `spec.values.env`, templated `${BASE_DOMAIN}` | **environment-specific and public** |
+
+**Exactly one source per variable.** Never define the same name in both places: an explicit `env:`
+entry silently overrides the same name arriving via `envFrom`, so an overlap hides which value is
+actually live.
+
+### Why the URLs are not in the Secret (the 2026-09-07 prod outage)
+
+Flux's `${BASE_DOMAIN}` postBuild substitution runs over the **rendered manifest text**; it can never
+reach inside an encrypted Secret. `OIDC_ISSUER_URL` and `OIDC_CALLBACK_URL` used to be keys in
+`headlamp-oidc-credentials.sops.yaml`, so both were frozen at the apex `home.keithjackson.dev`.
+Dev **is** the apex, so dev looked fine — but prod (`BASE_DOMAIN = prod.home.keithjackson.dev`) was
+pointed at **dev's** Keycloak, `192.168.1.53`, which sits on the dev LAN behind pfSense and is
+unroutable from prod's `192.168.2.0/24`. Every prod login failed with:
+
+```
+Get "https://keycloak.home.keithjackson.dev/realms/homelab/.well-known/openid-configuration":
+dial tcp 192.168.1.53:443: i/o timeout
+```
+
+An issuer URL and a callback URL are public, so they now live in cleartext in `helmrelease.yaml`
+where substitution works. Only the client secret stays encrypted. The same root cause and the same
+fix apply to Semaphore (`catalog/semaphore.yaml`, `SEMAPHORE_OIDC_PROVIDERS`).
+
+**[parity] `OIDC_ISSUER_URL` must equal the kube-apiserver's `oidc-issuer-url`**, which is an
+install-time k3s flag set from `k3s_base_domain` (`infra/ansible/roles/k3s_server/defaults/main.yml`,
+overridden per inventory group), *not* from `cluster-vars`. Headlamp forwards the user's `id_token`
+to the apiserver, so a mismatch 401s every request. Both derive from the same per-environment
+domain — dev `home.keithjackson.dev`, prod `prod.home.keithjackson.dev` — which is what keeps them
+in step; changing one without the other breaks login.
+
 ## Secrets
 
 - The confidential client secret lives SOPS-encrypted in
@@ -41,11 +84,6 @@ This keeps the apiserver OIDC config untouched (preferred over widening `--api-a
   placeholder) and mirrored in this namespace's `headlamp-oidc-credentials.sops.yaml`
   (`OIDC_CLIENT_SECRET`), which the chart `config.oidc.externalSecret` envFrom's. Same cross-namespace
   mirror pattern as grafana/gitea.
-- **Key names are load-bearing.** The chart `envFrom`s this Secret verbatim, so its keys become the
-  container env vars referenced by the chart's OIDC args (`-oidc-idp-issuer-url=$(OIDC_ISSUER_URL)`,
-  etc.). They must be exactly `OIDC_CLIENT_ID`, `OIDC_CLIENT_SECRET`, `OIDC_ISSUER_URL`, `OIDC_SCOPES`
-  (and `OIDC_CALLBACK_URL`) — **not** camelCase. A misnamed key leaves `$(OIDC_ISSUER_URL)`
-  unexpanded and OIDC login fails with `unsupported protocol scheme ""`.
 
 ## Break-glass
 
@@ -58,6 +96,6 @@ access if Keycloak/OIDC is down — the standard break-glass path.
 |---|---|---|
 | `namespace.yaml` | platform | `headlamp` namespace (`gateway-access=shared`; platform, not app-namespace) |
 | `helmrepository.yaml` / `helmrelease.yaml` | platform | Official `kubernetes-sigs/headlamp` chart + OIDC/RBAC values |
-| `headlamp-oidc-credentials.sops.yaml` | platform | SOPS OIDC config the chart envFrom's (decrypted by the `platform` Flux Kustomization) |
+| `headlamp-oidc-credentials.sops.yaml` | platform | SOPS OIDC **secret** the chart envFrom's — client id/scopes/secret only; the per-env URLs live in `helmrelease.yaml` `spec.values.env` |
 | `networkpolicy.yaml` | platform | default-deny baseline + Cilium ingress(gateway)/egress(apiserver+Keycloak) allows |
-| `httproute.yaml` | platform-config | Gateway API HTTPRoute for `headlamp.home.keithjackson.dev` (needs Gateway CRDs) |
+| `httproute.yaml` | platform-config | Gateway API HTTPRoute for `headlamp.${BASE_DOMAIN}` (needs Gateway CRDs) |