docs(arch): ADR-0035 — publish the stack through the existing labs Caddy (closes #177)

Records the decision #177 asked for, the other way round: the hypervisor has no
inbound path and the labs Caddy already holds 80/443 and the wildcard cert, so
the portals go through it over a reverse SSH tunnel instead of an in-cluster
edge. Covers keycloakUrl, KC_PROXY_HEADERS and the optional demo OTP autofill.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/architecture/adr-0035-public-access-through-the-labs-caddy.md

@@ -0,0 +1,108 @@
+# ADR-0035: The deployed stack is published through the existing labs Caddy
+
+- **Status:** Accepted
+- **Date:** 2026-09-25
+- **Deciders:** Respellion engineering
+- **Slice:** [#177](https://git.labs.respellion.tech/eho/register-referentie/issues/177) —
+  that issue proposed the opposite (an in-cluster Caddy edge); this ADR records why the
+  host-side option won. Implemented in #179, #180 and #181.
+
+## Context
+
+The stack deploys to a single-node Talos VM (ADR-0033, #175). Until now it was only usable
+through five SSH port-forwards: the portals' OIDC flow uses PKCE, PKCE needs
+`crypto.subtle`, and browsers expose that only in a **secure context**, meaning HTTPS or a
+`localhost` origin. A NodePort on the VM's address is neither. We want a URL a demo
+audience can simply open.
+
+Three facts about where things run shape the answer:
+
+- The Talos VM is a libvirt guest on a **Fedora hypervisor in the office**, behind NAT
+  with no public address. The only way in from outside is an existing reverse SSH tunnel
+  (`autossh-reverse-tunnel.service`) into an `openssh-server` container on the labs
+  server.
+- The **labs server** (public IP) already runs Caddy for `*.labs.respellion.tech`, with
+  the wildcard certificate (DNS-01 via Cloudflare) and ports 80/443. Every other labs
+  service is published there (repo `Infra`, `infra/development/`).
+- #177 proposed a Caddy **inside the cluster**, fed by a layer-4 forward on the host, so
+  that routing and certificates would be cluster state. That assumes the public IP is on
+  the hypervisor. It isn't: the hypervisor has no inbound path, and 80/443 on the labs
+  server are already taken by the labs Caddy.
+
+## Decision
+
+**Publish the portals and Keycloak through the existing labs Caddy. Carry the traffic to
+the cluster over a second reverse SSH tunnel from the hypervisor.**
+
+```
+browser ─https─▶ labs Caddy ─▶ openssh-server:3014x/30180
+        ─reverse SSH tunnel─▶ Fedora hypervisor ─▶ Talos NodePorts
+```
+
+- **Hostnames** under the existing wildcard: `big-register` (openbaar), `big-mijn`
+  (self-service), `big-behandel`, `big-beheer`, and `big-auth` (Keycloak, with `/admin*`
+  answered 404).
+- **Tunnel:** `big-portals-tunnel.service` on the hypervisor (repo `Infra`)
+  reverse-forwards the five browser-facing NodePorts into `openssh-server`. It is
+  separate from the access tunnel on `:6667`, so a failed forward can't cut SSH access.
+  Caddy joins the `openssh_default` network to reach the tunnel ends.
+- **Keycloak's issuer** is the public origin. The chart value `keycloakUrl` replaces
+  `host` + NodePort in one helper, `big.keycloakUrl`, which feeds both `KC_HOSTNAME` and
+  the portals' `config.json` authority, so the two cannot drift (ADR-0010). The deploy
+  workflow sets it from the `KEYCLOAK_URL` repository variable.
+- **`KC_PROXY_HEADERS=xforwarded`:** `KC_HOSTNAME_BACKCHANNEL_DYNAMIC` builds the token,
+  userinfo and certs URLs from the request. That request reaches Keycloak as plain HTTP,
+  so the URLs came out `http://` and browsers blocked them as mixed content. Trusting
+  Caddy's `X-Forwarded-Proto` keeps them HTTPS. In-cluster calls send no such header and
+  still use `keycloak:8080`.
+- **Demo MFA (optional):** `demo.otpAutofill` (`OTP_AUTOFILL`) makes the `big-demo` theme
+  (`infra/keycloak/themes/big-demo`) Keycloak's default. Its script fills in and submits
+  the medewerker OTP from the fixture secret (ADR-0031), so the step is visibly enforced
+  without an authenticator. It is off by default.
+
+### Alternatives considered
+
+- **In-cluster Caddy edge (#177, PR #178).** It would keep routes and certificates in
+  cluster state. But it needs a public inbound path to the hypervisor that doesn't exist,
+  plus a second certificate authority beside the labs Caddy, which already holds the
+  wildcard. Closed unmerged.
+- **Port-forward on the office router to the hypervisor.** This opens the office network
+  itself to the internet. Rejected.
+- **Move the cluster to a host with a public IP.** It would remove the tunnel, but it's a
+  bigger change than publishing one demo. It remains the natural step if the stack
+  outgrows a lab VM.
+- **Keep the SSH port-forwards.** Fine for one developer, but not something you can send
+  to someone.
+
+## Consequences
+
+**Positive**
+
+- Real hostnames and HTTPS, so PKCE works in any browser with no client-side setup.
+- No new certificate handling: the labs Caddy's wildcard covers the new hosts.
+- The chart stays edge-agnostic. With `keycloakUrl` empty it renders exactly as before,
+  so compose, CI and the `localhost` workflow are untouched.
+
+**Negative / costs**
+
+- **Routing lives outside the cluster**, in the Infra repo's Caddyfile. That is exactly
+  what #177 wanted to avoid. Adding a portal means changing three places: a NodePort in
+  the chart, a forward in the tunnel unit, and a host in the Caddyfile.
+- **Two SSH hops in the data path.** If the hypervisor or the tunnel is down, the
+  portals return 502 even though the cluster is healthy.
+- **One issuer string.** With `keycloakUrl` set, the `localhost` port-forward workflow
+  (runbook §5) can no longer log in.
+- **Keycloak trusts `X-Forwarded-*`** from anything that reaches it. Today that is only
+  in-cluster callers and the tunnel. `KC_PROXY_TRUSTED_ADDRESSES` can narrow it if the
+  NodePort is ever exposed more widely.
+- **The portals are public.** Anyone with the link can log in with the committed test
+  credentials, and with `OTP_AUTOFILL` on, no second factor stands in the way. That is
+  acceptable for synthetic data. Put the labs Caddy's Azure `authorize` in front of the
+  `big-*` hosts if the audience must be restricted.
+
+**Follow-up**
+
+- Runbook: `docs/runbooks/kubernetes-talos.md`, "Publishing through the labs Caddy".
+- Dev-mode Keycloak generates new signing keys on every restart, and the BFF re-fetches
+  them at most every 5 minutes, so expect a few minutes of 401s after a Keycloak restart.
+  Persisting Keycloak's database (runbook §6) would remove that.

docs/runbooks/kubernetes-talos.md

@@ -403,6 +403,8 @@ upgrade path.
 
 ## Publishing through the labs Caddy
 
+Why this route and not an in-cluster edge: [ADR-0035](../architecture/adr-0035-public-access-through-the-labs-caddy.md).
+
 The portals can be reached on real hostnames through the Caddy that already fronts
 `*.labs.respellion.tech` (repo `Infra`, `infra/development/`). The chain:
 

mkdocs.yml

@@ -56,6 +56,7 @@ nav:
       - "ADR-0032: Werkbak live refresh": architecture/adr-0032-werkbak-live-refresh.md
       - "ADR-0033: Kubernetes via one Helm chart": architecture/adr-0033-kubernetes-via-one-helm-chart.md
       - "ADR-0034: Caddy serves the portals": architecture/adr-0034-caddy-serves-the-portals.md
+      - "ADR-0035: Public access through the labs Caddy": architecture/adr-0035-public-access-through-the-labs-caddy.md
   - FDS-architectuur:
       - Overzicht: architecture/fds/README.md
       - Componentview (L3): architecture/fds/c4-component-view.md