docs(infra): document MFA on the medewerker realm + ADR-0031 (refs #132)

Runbook gains an MFA section and how to get a code; synthetic-data lists the fixture
TOTP secret and the extra grant parameter; demo-script gains the S-15c note and its
staff logins now mention the second factor. check_realms.py grows an 'otp' argument
that prints a current code for a manual demo.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/architecture/adr-0031-mfa-on-the-medewerker-realm.md

@@ -0,0 +1,49 @@
+# ADR-0031 — MFA on the medewerker realm, with a fixture TOTP secret
+
+- **Status:** Accepted
+- **Date:** 2026-09-03
+- **Slice:** S-15c (Gitea #132)
+
+## Context
+
+Staff (behandelaar, teamlead, beheerder) act on citizens' registrations and on the ACL's
+default-fill: the highest-privilege logins in the platform. The medewerker realm protected
+them with a password alone, while the citizen realms (digid, eherkenning, eidas) mock
+brokers that carry their own assurance levels. A reference application that demonstrates a
+government architecture should show MFA on the staff realm.
+
+Two things had to be decided: **how** to enforce OTP in a realm export, and **how the
+automated checks and a human demo obtain a code** — the e2e drives a real browser login and
+`make keycloak-smoke` drives a real password grant, so neither can scan a QR.
+
+## Decision
+
+**Enforce OTP by giving every seeded medewerker a TOTP credential**, rather than replacing
+Keycloak's browser flow with a copy whose OTP execution is `REQUIRED`.
+
+Keycloak's stock `browser` and `direct grant` flows both contain a *conditional OTP*
+subflow that fires when the user has an OTP credential. Seeding the credential therefore
+turns the challenge on for every seeded user, in both flows, without duplicating ~40 lines
+of flow JSON into the export. `CONFIGURE_TOTP` is additionally set as a **default required
+action**, so a medewerker created later must enrol before their first login.
+
+**The seeded secret is a fixed, committed fixture** (`BIGMEDEWERKEROTPSEED`) shared by all
+medewerkers. Codes are then computable: `infra/keycloak/check_realms.py` (Python, stdlib
+`hmac`) and `tests/e2e/medewerker-login.ts` (Node `crypto`) each implement RFC 6238 in
+about six lines — no OTP dependency on either side, and no enrolment step in the tests.
+
+## Consequences
+
+- A password alone no longer yields a token on the medewerker realm; `check_realms.py`
+  asserts that refusal, so the enforcement cannot silently regress.
+- Every medewerker login in the e2e goes through `loginMedewerker()`, which submits the OTP
+  form. New staff specs must use it.
+- **The secret is public.** It is a demo fixture and worthless outside this synthetic
+  stack, in the same class as the committed `test123` passwords and the mock DigiD broker.
+  A real deployment enrols per-user authenticators (or federates to DigiD Machtigen /
+  eHerkenning at the required assurance level) and seeds no credentials at all.
+- Enforcement is *effectively* realm-wide but *technically* per-user: the conditional
+  subflow is what fires. A medewerker whose OTP credential were removed would fall back to
+  the required action at next login (enrol, then challenge) rather than skipping MFA — an
+  acceptable equivalence for this purpose, and the reason the required action is set.
+- Reversal is a one-file edit: drop the `otp` credentials and the `requiredActions` block.

docs/demo-script.md

@@ -140,7 +140,8 @@ zaaktype cache). Store is in-memory: an edit reverts to the configured env on re
 
 ```bash
 make up
-# 1. Log in as bram-beheerder / test123 → "Default-fill" tab → change a value → Opslaan.
+# 1. Log in as bram-beheerder / test123 + OTP (`python3 infra/keycloak/check_realms.py otp`)
+#    → "Default-fill" tab → change a value → Opslaan.
 open http://localhost:8143/default-fill
 #
 # 2. Automated: the ACL uses the current default-fill per zaak (unit) and the endpoints are behind the
@@ -161,7 +162,8 @@ directly (ADR-0025); managing the default-fill config (S-15b) and MFA (S-15c) co
 
 ```bash
 make up
-# 1. Log in as bram-beheerder / test123 → the catalogus lists the published zaaktypen.
+# 1. Log in as bram-beheerder / test123 + OTP (`python3 infra/keycloak/check_realms.py otp`)
+#    → the catalogus lists the published zaaktypen.
 open http://localhost:8143
 #
 # 2. Automated (a CI verify-stack e2e): a beheerder logs in and sees BIG-REGISTRATIE.
@@ -304,7 +306,8 @@ make verify-local     # → "OK — a fresh local stack completed the flow with
 
 # 3. Or by hand in the browser: log in at http://localhost:8140 (jan-burger / test123), submit +
 #    upload a PDF, then approve it in the werkbak at http://localhost:8142 (merel-behandelaar /
-#    test123); it shows as INGESCHREVEN in the openbaar register at http://localhost:8141.
+#    test123 + OTP, see S-15c); it shows as INGESCHREVEN in the openbaar register at
+#    http://localhost:8141.
 ```
 
 > The zaaktype is discovered by the ACL itself since S-27 (below); `local-seed`'s `acl.env` now
@@ -589,7 +592,7 @@ or **afwijzen** — which also completes the Beoordelen task so the process adva
 
 ```text
 # 1. Open the behandel portal and log in as a behandelaar (medewerker realm):
-#    http://localhost:8142/   →  merel-behandelaar / test123
+#    http://localhost:8142/   →  merel-behandelaar / test123 + OTP
 #
 # 2. The werkbak lists the registrations awaiting beoordeling (referentie / bsn / status).
 #    Find the reference from the submit confirmation and click "Goedkeuren" on that row.
@@ -812,3 +815,32 @@ make verify-domain     # → "the timed-out registration's zaak was cancelled to
 `POST /annuleringen` → ZGW `resultaten` + `statussen` (Geannuleerd); the aggregate then moves to
 `Verlopen`. The ACL cancels the zaak **before** the aggregate is expired, so a failed ZGW call leaves the
 job for redelivery rather than diverging the two (ADR-0019).
+
+---
+
+## S-15c — MFA on the medewerker realm (#132, ADR-0031)
+
+**Outcome:** staff logins (behandel + beheer portals) need a **second factor**. The medewerker realm
+seeds every medewerker with a TOTP credential, so Keycloak's conditional-OTP step challenges them in
+both the browser flow and the direct grant; a password alone no longer yields a token. `CONFIGURE_TOTP`
+is a default required action, so a medewerker added later must enrol first. Citizen realms (digid,
+eherkenning, eidas) are unchanged — they mock brokers that carry their own assurance.
+
+```bash
+# 1. Manual: log in to the behandel portal. After username + password Keycloak asks for a code.
+python3 infra/keycloak/check_realms.py otp   # a valid code, right now
+open http://localhost:8142                   # merel-behandelaar / test123 + that code
+#
+# 2. Automated: the realm smoke check asserts the password alone is REFUSED, then that
+#    password + TOTP succeeds and still carries the behandelaar role:
+make keycloak-smoke    # → "medewerker  merel-behandelaar  password-only login refused [OK]"
+#
+# 3. End-to-end: every staff login in the e2e goes through the OTP prompt (loginMedewerker):
+make verify-e2e        # → registration.spec (behandelaar approves), catalogus.spec, default-fill.spec
+```
+
+**The path:** the seeded `otp` credential in `infra/keycloak/realms/medewerker-realm.json` activates
+Keycloak's stock conditional-OTP subflow — no custom browser flow. The fixture secret is shared and
+committed on purpose so the checks can compute codes; a real deployment enrols per-user authenticators
+(ADR-0031).
+

docs/runbooks/keycloak.md

@@ -23,6 +23,9 @@ login per realm and asserts the identifying claim:
 | eidas | pierre-dupont | `eidas_id` |
 | medewerker | merel-behandelaar | role `behandelaar` |
 
+The medewerker row also asserts that the password **alone** is refused — that realm
+enforces MFA (below).
+
 All test users / credentials are in [../synthetic-data.md](../synthetic-data.md).
 
 ## Notes
@@ -35,3 +38,30 @@ All test users / credentials are in [../synthetic-data.md](../synthetic-data.md)
 - **Image** pinned to `quay.io/keycloak/keycloak:26.1`.
 - Claims are injected by OIDC protocol mappers on `big-portal` (user attribute → token
   claim); `medewerker` roles come through `realm_access.roles`.
+
+## MFA on the medewerker realm (S-15c)
+
+Staff logins (behandel + beheer portals) need a second factor; citizen/company realms
+(digid, eherkenning, eidas) do not. Two halves in `medewerker-realm.json`:
+
+- Every seeded medewerker carries a **TOTP credential** with the fixture secret
+  `BIGMEDEWERKEROTPSEED`, so Keycloak's built-in *conditional OTP* step fires on every
+  login — browser flow (an `#otp` prompt after the password) and direct grant (a `totp`
+  form field) alike.
+- `CONFIGURE_TOTP` is a **default required action**, so any medewerker added later must
+  enrol an authenticator before the first login.
+
+See [../architecture/adr-0031-mfa-on-the-medewerker-realm.md](../architecture/adr-0031-mfa-on-the-medewerker-realm.md).
+
+### Getting a code
+
+```bash
+python3 infra/keycloak/check_realms.py otp   # prints a valid 6-digit code right now
+```
+
+Or enrol a phone once: the secret in base32 is `IJEUOTKFIRCVORKSJNCVET2UKBJUKRKE`
+(`otpauth://totp/medewerker?secret=IJEUOTKFIRCVORKSJNCVET2UKBJUKRKE`). The e2e computes its
+own code in `tests/e2e/medewerker-login.ts`.
+
+**Fixture only.** A shared, committed secret is a demo convenience, never a production
+posture — see the ADR's consequences.

docs/synthetic-data.md

@@ -19,6 +19,11 @@ All test users share the password **`test123`**.
 | `eidas` | eIDAS (EU) | `pierre-dupont` | `eidas_id` = `FR/NL/AB-1234-5678` |
 | `medewerker` | Internal staff | `merel-behandelaar` | role `behandelaar` |
 | `medewerker` | Internal staff | `tom-teamlead` | roles `behandelaar`, `teamlead` |
+| `medewerker` | Internal staff | `bram-beheerder` | role `beheerder` |
+
+`medewerker` users additionally need a **second factor**: that realm enforces MFA (S-15c,
+ADR-0031). All three share the fixture TOTP secret `BIGMEDEWERKEROTPSEED`; print a current
+code with `python3 infra/keycloak/check_realms.py otp`.
 
 The identifying claims are injected via OIDC protocol mappers on `big-portal`
 (user-attribute → token claim); `medewerker` roles appear in `realm_access.roles`.
@@ -32,5 +37,8 @@ curl -s -X POST \
   -d username=jan-burger -d password=test123 -d scope=openid | jq -r .access_token
 ```
 
+For a `medewerker` user, add `-d totp=$(python3 infra/keycloak/check_realms.py otp)` —
+without it the grant is refused with `invalid_grant`.
+
 Decode the JWT payload to see the `bsn` claim. `make keycloak-smoke` checks every realm
 automatically.

infra/keycloak/check_realms.py

@@ -86,4 +86,9 @@ def main():
 
 
 if __name__ == "__main__":
+    # `check_realms.py otp` prints a current code for the fixture secret — what a human demoing
+    # the medewerker portals types at Keycloak's OTP prompt (docs/runbooks/keycloak.md).
+    if len(sys.argv) > 1 and sys.argv[1] == "otp":
+        print(totp())
+    else:
         main()