docs(architecture): ADR-0004 — Reqnroll as BDD framework (refs #5)

Record the choice of Reqnroll.xUnit for the acceptance layer introduced in
S-04, and register the previously-unlisted ADR-0002/0003 in the MkDocs nav.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitignore

@@ -5,6 +5,9 @@ obj/
 [Rr]elease/
 *.user
 
+# Reqnroll-generated test code (regenerated from *.feature on build)
+*.feature.cs
+
 # Test results / coverage
 [Tt]est[Rr]esults/
 *.trx

Makefile

@@ -5,11 +5,18 @@
 # `make ci` locally runs exactly what the pipeline runs — no drift. Until a
 # self-hosted runner is registered, `make ci` is the gate (see docs/runbooks/ci.md).
 
-SLN        := services/bff/Bff.slnx
+SLN        := register-referentie.slnx
 COMPOSE    := infra/docker-compose.yml
 HEALTH_URL := http://localhost:8080/health
-OZ_COMPOSE := infra/openzaak/docker-compose.yml
-OZ_BASE    := http://localhost:8000
+OZ_COMPOSE  := infra/openzaak/docker-compose.yml
+OZ_BASE     := http://localhost:8000
+NRC_COMPOSE := infra/opennotificaties/docker-compose.yml
+NRC_BASE    := http://localhost:8001
+KC_COMPOSE  := infra/keycloak/docker-compose.yml
+KC_BASE     := http://localhost:8180
+FL_COMPOSE  := infra/flowable/docker-compose.yml
+FL_BASE     := http://localhost:8090/flowable-rest/service
+STACK_FILES := -f $(OZ_COMPOSE) -f $(NRC_COMPOSE)
 
 # On a rootless Podman dev box, point Docker CLI/Compose at the Podman socket —
 # but only if that socket exists and DOCKER_HOST isn't already set, so real
@@ -21,7 +28,7 @@ export DOCKER_HOST := unix://$(PODMAN_SOCK)
 endif
 endif
 
-.PHONY: ci lint build unit smoke down changelog openzaak-up openzaak-smoke openzaak-seed openzaak-down help
+.PHONY: ci lint build unit smoke down changelog openzaak-up openzaak-smoke openzaak-seed openzaak-down stack-up stack-smoke stack-down keycloak-up keycloak-smoke keycloak-down flowable-up flowable-smoke flowable-down help
 
 ## ci: run the full pipeline — lint, build, unit, smoke (mirrors Gitea Actions)
 ci: lint build unit smoke
@@ -82,6 +89,58 @@ openzaak-seed: openzaak-up
 openzaak-down:
 	docker compose -f $(OZ_COMPOSE) down --volumes
 
+## stack-up: start OpenZaak + Open Notificaties together (shared network)
+stack-up:
+	docker compose $(STACK_FILES) up -d
+
+## stack-smoke: start both, assert OpenZaak (403/302/200) and NRC (302) are reachable
+stack-smoke: stack-up
+	@bash -c 'set -e; \
+	  echo "waiting for OpenZaak + Open Notificaties..."; \
+	  for i in $$(seq 1 60); do \
+	    oz=$$(curl -s -o /dev/null -w "%{http_code}" $(OZ_BASE)/admin/ || true); \
+	    nrc=$$(curl -s -o /dev/null -w "%{http_code}" $(NRC_BASE)/admin/ || true); \
+	    [ "$$oz" = "302" ] && [ "$$nrc" = "302" ] && break; sleep 3; done; \
+	  z=$$(curl -s -o /dev/null -w "%{http_code}" $(OZ_BASE)/zaken/api/v1/zaken); \
+	  echo "OpenZaak /zaken (unauth) -> $$z (expect 403)"; test "$$z" = "403"; \
+	  echo "OpenZaak /admin/         -> $$oz (expect 302)"; test "$$oz" = "302"; \
+	  echo "Open Notificaties /admin/-> $$nrc (expect 302)"; test "$$nrc" = "302"; \
+	  echo "stack smoke OK"'
+
+## stack-down: stop and remove both stacks (wipes data)
+stack-down:
+	docker compose $(STACK_FILES) down --volumes
+
+## keycloak-up: start Keycloak with the four imported realms
+keycloak-up:
+	docker compose -f $(KC_COMPOSE) up -d
+
+## keycloak-smoke: start Keycloak, then verify each realm logs in + returns its claim
+keycloak-smoke: keycloak-up
+	@bash -c 'for i in $$(seq 1 60); do \
+	    c=$$(curl -s -o /dev/null -w "%{http_code}" $(KC_BASE)/realms/digid/.well-known/openid-configuration || true); \
+	    [ "$$c" = "200" ] && break; sleep 3; done; echo "Keycloak ready ($$c)"'
+	python3 infra/keycloak/check_realms.py
+
+## keycloak-down: stop and remove Keycloak
+keycloak-down:
+	docker compose -f $(KC_COMPOSE) down --volumes
+
+## flowable-up: start Flowable (deploys registratie.bpmn on boot)
+flowable-up:
+	docker compose -f $(FL_COMPOSE) up -d
+
+## flowable-smoke: start Flowable, then verify a started instance waits on the external task
+flowable-smoke: flowable-up
+	@bash -c 'for i in $$(seq 1 80); do \
+	    c=$$(curl -s -o /dev/null -w "%{http_code}" -u rest-admin:test $(FL_BASE)/repository/process-definitions?key=registratie || true); \
+	    [ "$$c" = "200" ] && break; sleep 3; done; echo "Flowable ready ($$c)"'
+	python3 infra/flowable/verify.py
+
+## flowable-down: stop and remove Flowable
+flowable-down:
+	docker compose -f $(FL_COMPOSE) down --volumes
+
 ## help: list available targets
 help:
 	@grep -E '^## ' $(MAKEFILE_LIST) | sed 's/^## //'

docs/architecture/adr-0003-default-fill.md

@@ -0,0 +1,44 @@
+# ADR-0003: ACL default-fill strategy
+
+- **Status:** Accepted
+- **Date:** 2026-06-04
+- **Deciders:** Respellion engineering
+- **Relates to:** S-04 (#5); builds on ADR-0001 (loose coupling)
+
+## Context
+
+The ACL is the only code that talks to ZGW APIs (ADR-0001 / CLAUDE.md §8.1). When the
+domain asks it to "open a zaak", the domain payload is intentionally free of ZGW
+specifics — it carries domain facts (e.g. the registrant's BSN), not OpenZaak fields. But
+OpenZaak's `POST /zaken` requires ZGW-mandatory fields: `bronorganisatie`,
+`verantwoordelijkeOrganisatie`, `startdatum`, `vertrouwelijkheidaanduiding`, and a
+`zaaktype` URL. Something has to supply those, and it must not leak into the domain.
+
+## Decision
+
+**The ACL default-fills the ZGW-mandatory zaak fields; the domain never sees them.**
+
+- `bronorganisatie`, `verantwoordelijkeOrganisatie`, `vertrouwelijkheidaanduiding`, and the
+  `zaaktype` URL come from **ACL configuration** (`AclDefaults` options) — not hardcoded,
+  not from the domain. This keeps them operationally manageable (the beheer portal will
+  edit them in S-15) and environment-specific (the seeded BIG zaaktype URL differs per env).
+- `startdatum` is derived from an injected **clock** (today's date), so it is
+  deterministic in tests.
+- The mapping from domain payload → ZGW `ZaakRequest` lives entirely inside the ACL
+  (`Application` builds the request from payload + defaults; `Infrastructure` serialises and
+  POSTs it). No other service constructs ZGW payloads or URLs.
+
+## Consequences
+
+- **Positive:** the domain stays ZGW-agnostic; ZGW knowledge is in one named place; defaults
+  are config (testable, env-specific, later editable via the beheer portal).
+- **Cost:** the ACL must be configured per environment (the seeded zaaktype URL, the
+  organisation RSINs). Missing/invalid config fails fast at the ACL boundary.
+- **Follow-ups:** mapping the BSN onto the zaak (eigenschap/rol), status transitions, and
+  documents are explicitly out of scope for S-04 and get their own slices.
+
+## Alternatives considered
+
+- **Defaults in the domain payload** — rejected: leaks ZGW concerns into the domain,
+  violating ADR-0001.
+- **Hardcoded defaults in code** — rejected: not env-specific, not operationally editable.

docs/architecture/adr-0004-bdd-framework.md

@@ -0,0 +1,52 @@
+# ADR-0004: Reqnroll as the BDD acceptance framework
+
+- **Status:** Accepted
+- **Date:** 2026-06-04
+- **Deciders:** Respellion engineering
+- **Relates to:** S-04 (#5); supports CLAUDE.md §3 (BDD at the use-case level) and §11 (tests pyramid)
+
+## Context
+
+CLAUDE.md §11 mandates that each user-visible flow is driven by a Gherkin acceptance
+scenario living in `tests/acceptance/`, and §3 names "BDD at the use-case level" as a core
+engineering principle. The foundational slices (S-00…S-03) added no acceptance layer; S-04
+is the first slice with real domain behaviour to drive, so it is where the BDD framework is
+introduced. We need a .NET tool that:
+
+- parses Gherkin `.feature` files and binds steps to C#,
+- integrates with the existing xUnit test runner (the repo standardises on xUnit), so
+  acceptance tests run under the same `dotnet test` / `make ci` gate as everything else,
+- is actively maintained on modern .NET (we target net10.0).
+
+## Decision
+
+**Use [Reqnroll](https://reqnroll.net/) (`Reqnroll.xUnit`) for acceptance tests.**
+
+- Reqnroll is the actively-maintained, open-source successor to SpecFlow (which is no longer
+  maintained). It keeps the same Gherkin + `[Binding]` model, so the knowledge transfers.
+- `Reqnroll.xUnit` generates one xUnit test per scenario, so acceptance tests are discovered
+  and run by the same runner as the unit tests — no second test framework, no extra CI step.
+- Acceptance projects live under `tests/acceptance/` per the PRD §9 layout. Generated
+  `*.feature.cs` files are build artefacts and are git-ignored.
+
+## Consequences
+
+- **Positive:** one assertion/runner stack (xUnit) across unit and acceptance tests; scenarios
+  are written in business language (Dutch domain terms inline) and reviewed as the slice's
+  contract; maintained tooling on net10.0.
+- **Cost:** a new dependency (`Reqnroll.xUnit`) and its xUnit v2 transitive graph. Reqnroll
+  pulls `xunit.core` but not the assertion library, so the `xunit` metapackage is referenced
+  explicitly to get `Assert`.
+- **Replaceable by:** hand-written xUnit "scenario" tests with a Given/When/Then helper, at
+  the cost of losing Gherkin as the shared, readable contract — which is the whole point of §3.
+- **Follow-ups:** the real-OpenZaak integration test (Testcontainers) and the Stryker mutation
+  baseline for S-04 are tracked as their own issues split off #5.
+
+## Alternatives considered
+
+- **SpecFlow** — rejected: unmaintained and without an official net10.0 story; Reqnroll is its
+  drop-in successor.
+- **Plain xUnit Given/When/Then helpers** — rejected for user-visible flows: loses the
+  business-readable Gherkin contract that §3/§11 require. Still fine for unit-level tests.
+- **Xunit.Gherkin.Quick** — rejected: lighter but less featureful (no hooks/scoped contexts,
+  smaller community) than Reqnroll.

docs/runbooks/flowable.md

@@ -0,0 +1,40 @@
+# Flowable runbook
+
+Flowable (`infra/flowable/docker-compose.yml`) runs the **flowable-rest** engine on
+Postgres. The `workflows/registratie.bpmn` model is deployed via the REST API at boot by
+the `flowable-init` container. Host port **:8090**; REST API under
+`http://localhost:8090/flowable-rest/service/` (basic auth **rest-admin / test**, dev only).
+
+## The model — `registratie`
+
+A minimal "Registratie ontvangen" process: **start → external-worker task
+`OpenZaakAanmaken` → end**. The external task is where the Workflow Client / ACL will
+later create the zaak in OpenZaak (S-04/S-05); for now a started instance parks there.
+
+## Quick test (`make`)
+
+```bash
+make flowable-up      # start engine + deploy registratie.bpmn on boot
+make flowable-smoke   # start + verify a new instance waits on the external task
+make flowable-down    # stop + wipe
+```
+
+`make flowable-smoke` runs `infra/flowable/verify.py`, which:
+1. waits for the `registratie` process definition to be deployed,
+2. starts an instance and asserts it did **not** end immediately,
+3. asserts an execution is parked at activity **`OpenZaakAanmaken`**,
+4. deletes the test instance.
+
+## Notes
+
+- **Deploy on boot** is idempotent: `flowable-init` skips if a deployment named
+  `registratie` already exists (so restarts on the same volume don't pile up versions).
+- **Dev creds:** `rest-admin` / `test`. Override via the flowable-rest app config for
+  anything beyond local dev.
+- **Image** `flowable/flowable-rest:latest` — pin a tag when stabilising.
+- Start an instance by hand:
+  ```bash
+  curl -s -u rest-admin:test -H 'Content-Type: application/json' \
+    -d '{"processDefinitionKey":"registratie"}' \
+    http://localhost:8090/flowable-rest/service/runtime/process-instances
+  ```

docs/runbooks/keycloak.md

@@ -0,0 +1,37 @@
+# Keycloak runbook
+
+Keycloak (`infra/keycloak/docker-compose.yml`) runs in dev mode with four realms
+imported at boot from `infra/keycloak/realms/`: **digid**, **eherkenning**, **eidas**,
+**medewerker**. It mocks the Dutch identity brokers so portals can do real OIDC logins
+locally. Host port **:8180**.
+
+## Quick test (`make`)
+
+```bash
+make keycloak-up      # start Keycloak + import realms (~30-60s first boot)
+make keycloak-smoke   # start + verify every realm logs in and returns its claim
+make keycloak-down    # stop + wipe
+```
+
+`make keycloak-smoke` runs `infra/keycloak/check_realms.py`, which does a password-grant
+login per realm and asserts the identifying claim:
+
+| Realm | User | Claim asserted |
+|---|---|---|
+| digid | jan-burger | `bsn` |
+| eherkenning | acme-ondernemer | `kvk` |
+| eidas | pierre-dupont | `eidas_id` |
+| medewerker | merel-behandelaar | role `behandelaar` |
+
+All test users / credentials are in [../synthetic-data.md](../synthetic-data.md).
+
+## Notes
+
+- **Admin console:** <http://localhost:8180/> — `admin` / `admin` (dev only).
+- **Client `big-portal`** is public with `standardFlowEnabled` (browser redirect login)
+  *and* `directAccessGrantsEnabled` (password grant, used by the smoke test).
+- **Dev store:** in-memory H2 via `start-dev`; realms re-import on each boot, so changes
+  made in the admin UI don't persist. Edit the realm JSONs to make durable changes.
+- **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`.

docs/runbooks/opennotificaties.md

@@ -0,0 +1,44 @@
+# Open Notificaties (NRC) runbook
+
+The Open Notificaties stack (`infra/opennotificaties/docker-compose.yml`) is a lean
+adaptation of the upstream dev compose: PostGIS db, redis (also the Celery broker), a
+one-shot migrate-init, the API, and a celery worker. It shares the **`cg`** Docker
+network with the OpenZaak stack so the two can reach each other by service name.
+
+NRC is published on host **:8001** (OpenZaak holds :8000).
+
+## Quick test (`make`) — both platforms together
+
+```bash
+make stack-up      # OpenZaak + Open Notificaties on the shared network
+make stack-smoke   # start both + assert reachable (OZ 403/302/200, NRC 302)
+make stack-down    # stop + wipe both
+```
+
+`make stack-smoke` runs `docker compose -f infra/openzaak/... -f infra/opennotificaties/... up -d`
+and asserts:
+
+| Check | Expected |
+|---|---|
+| OpenZaak `GET /zaken/api/v1/zaken` (no JWT) | 403 (auth enforced) |
+| OpenZaak `GET /admin/` | 302 |
+| Open Notificaties `GET /admin/` | 302 |
+
+NRC admin UI: <http://localhost:8001/admin/> (dev superuser **admin / admin**).
+
+## Notification wiring is deferred to S-06
+
+Both platforms are **up and reachable**, but OpenZaak→NRC notification *delivery* is not
+wired yet, and OpenZaak still runs with `NOTIFICATIONS_DISABLED=true`. The bidirectional
+auth wiring (NRC `setup_configuration`: Services + Authorization to OpenZaak's
+Autorisaties API + JWT secrets + Kanalen + Abonnementen; OpenZaak's NotificationConfig)
+lands with **S-06 (Event Subscriber)** — the slice that actually consumes events. NRC's
+`setup_configuration/data.yaml` is intentionally minimal (migrations only) until then.
+
+This matches S-01's acceptance, which asks only that the platforms *come up in compose*
+and a health check confirms them reachable.
+
+## Prerequisites
+
+Same rootless-Podman setup as the rest of the repo — see [ci.md](ci.md) and
+[openzaak.md](openzaak.md). `systemctl --user start podman.socket` once per session.

docs/runbooks/openzaak.md

@@ -66,8 +66,9 @@ The Makefile auto-points `DOCKER_HOST` at the Podman socket when it exists, so t
 - **Not in `make ci`.** The OpenZaak smoke is a separate, heavier check (large image
   pull + migrations); it is intentionally kept out of `make ci` so the core gate
   stays fast. Run `make openzaak-smoke` when you touch the OpenZaak stack.
-- **Notifications disabled.** `NOTIFICATIONS_DISABLED=true` until Open Notificaties
-  (NRC) lands in S-01-c — otherwise ZTC writes 500 trying to notify. Re-enable then.
+- **Notifications disabled.** `NOTIFICATIONS_DISABLED=true` — otherwise ZTC writes 500
+  trying to notify. Open Notificaties is now up (see [opennotificaties.md](opennotificaties.md)),
+  but OZ→NRC delivery wiring + re-enabling lands with **S-06**.
 - **Zaaktype is a concept**, not published (publishing needs roltypen/statustypen/
   resultaattypen — beyond the lean seed). List with `?status=alles`.
 - **Image tag.** Currently `openzaak/open-zaak:latest` via `${OPENZAAK_TAG}`; pin to

docs/synthetic-data.md

@@ -0,0 +1,35 @@
+# Synthetic data
+
+All credentials here are **dev-only** synthetic test data — never real personal data,
+never used outside local development.
+
+## Keycloak realms (S-02)
+
+Keycloak runs at <http://localhost:8180> (admin console: **admin / admin**). Four realms
+are imported at boot from `infra/keycloak/realms/`. Each has a public OIDC client
+**`big-portal`** (standard flow + direct access grants enabled, redirect URIs `*` for dev).
+
+All test users share the password **`test123`**.
+
+| Realm | Mimics | User | Identifying claim |
+|---|---|---|---|
+| `digid` | DigiD (burgers) | `jan-burger` | `bsn` = `123456782` |
+| `eherkenning` | eHerkenning (bedrijven) | `acme-ondernemer` | `kvk` = `12345678` |
+| `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` |
+
+The identifying claims are injected via OIDC protocol mappers on `big-portal`
+(user-attribute → token claim); `medewerker` roles appear in `realm_access.roles`.
+
+## Get a token (for testing)
+
+```bash
+curl -s -X POST \
+  http://localhost:8180/realms/digid/protocol/openid-connect/token \
+  -d grant_type=password -d client_id=big-portal \
+  -d username=jan-burger -d password=test123 -d scope=openid | jq -r .access_token
+```
+
+Decode the JWT payload to see the `bsn` claim. `make keycloak-smoke` checks every realm
+automatically.

infra/flowable/docker-compose.yml

@@ -0,0 +1,65 @@
+# Flowable (S-03): the flowable-rest engine on Postgres.
+# The registratie.bpmn model is deployed via the REST API on startup by flowable-init.
+#
+#   docker compose -f infra/flowable/docker-compose.yml up -d
+#   # REST API (basic auth) under http://localhost:8090/flowable-rest/service/
+#
+# Host port 8090 (8000/8001/8080/8180 are taken by OpenZaak/NRC/BFF/Keycloak).
+services:
+  flowable-db:
+    image: docker.io/library/postgres:16
+    environment:
+      POSTGRES_USER: flowable
+      POSTGRES_PASSWORD: flowable
+      POSTGRES_DB: flowable
+    volumes:
+      - flowable-db:/var/lib/postgresql/data
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U flowable -d flowable"]
+      interval: 5s
+      timeout: 3s
+      retries: 10
+    networks: [cg]
+
+  flowable-rest:
+    image: docker.io/flowable/flowable-rest:latest
+    environment:
+      SPRING_DATASOURCE_DRIVER-CLASS-NAME: org.postgresql.Driver
+      SPRING_DATASOURCE_URL: jdbc:postgresql://flowable-db:5432/flowable
+      SPRING_DATASOURCE_USERNAME: flowable
+      SPRING_DATASOURCE_PASSWORD: flowable
+    ports:
+      - "8090:8080"
+    depends_on:
+      flowable-db:
+        condition: service_healthy
+    networks: [cg]
+
+  # Deploys workflows/registratie.bpmn via the REST API once flowable-rest is up.
+  # Idempotent: skips if a deployment named "registratie" already exists.
+  flowable-init:
+    image: docker.io/curlimages/curl:latest
+    restart: "no"
+    volumes:
+      - ../../workflows/registratie.bpmn:/work/registratie.bpmn:ro,z
+    command:
+      - sh
+      - -c
+      - |
+        base=http://flowable-rest:8080/flowable-rest/service/repository/deployments
+        until curl -sf -u rest-admin:test "$$base" >/dev/null 2>&1; do echo "waiting for flowable-rest..."; sleep 3; done
+        if curl -s -u rest-admin:test "$$base?name=registratie" | grep -q '"name":"registratie"'; then
+          echo "registratie already deployed; skip"
+        else
+          curl -sf -u rest-admin:test -F 'file=@/work/registratie.bpmn;filename=registratie.bpmn' "$$base" >/dev/null && echo "deployed registratie"
+        fi
+    depends_on:
+      flowable-rest:
+        condition: service_started
+    networks: [cg]
+
+volumes:
+  flowable-db:
+
+networks:
+  cg:

infra/flowable/verify.py

@@ -0,0 +1,54 @@
+#!/usr/bin/env python3
+"""Smoke-check Flowable: the registratie process is deployed, and starting an
+instance parks it on the OpenZaakAanmaken external task. Stdlib only.
+"""
+import base64, json, sys, time, urllib.error, urllib.request
+
+BASE = "http://localhost:8090/flowable-rest/service"
+AUTH = "Basic " + base64.b64encode(b"rest-admin:test").decode()
+
+
+def call(method, path, payload=None):
+    data = json.dumps(payload).encode() if payload is not None else None
+    req = urllib.request.Request(BASE + path, data=data, method=method, headers={
+        "Authorization": AUTH, "Content-Type": "application/json", "Accept": "application/json"})
+    with urllib.request.urlopen(req, timeout=30) as r:
+        return r.status, json.loads(r.read() or "null")
+
+
+def main():
+    # 1. process definition deployed? (wait for the async init-container deploy)
+    defs = {"total": 0}
+    for _ in range(40):
+        _, defs = call("GET", "/repository/process-definitions?key=registratie")
+        if defs["total"] >= 1:
+            break
+        time.sleep(3)
+    assert defs["total"] >= 1, "registratie process definition not deployed"
+    print(f"process definition 'registratie' deployed (total={defs['total']})")
+
+    # 2. start an instance
+    st, pi = call("POST", "/runtime/process-instances", {"processDefinitionKey": "registratie"})
+    assert st == 201, f"start failed: {st} {pi}"
+    pid = pi["id"]
+    assert pi.get("ended") is False, "instance ended immediately — external task not reached"
+    print(f"started instance {pid} (ended={pi.get('ended')})")
+
+    # 3. waiting on the external task?
+    _, ex = call("GET", f"/runtime/executions?processInstanceId={pid}")
+    activities = [e.get("activityId") for e in ex["data"]]
+    assert "OpenZaakAanmaken" in activities, f"not waiting at OpenZaakAanmaken: {activities}"
+    print(f"instance is waiting at the external task: {activities}")
+
+    # 4. cleanup
+    try:
+        call("DELETE", f"/runtime/process-instances/{pid}")
+        print("cleaned up instance")
+    except urllib.error.HTTPError:
+        pass
+
+    print("flowable smoke OK")
+
+
+if __name__ == "__main__":
+    main()

infra/keycloak/check_realms.py

@@ -0,0 +1,60 @@
+#!/usr/bin/env python3
+"""Smoke-check the Keycloak realms: each realm's OIDC login works (password grant)
+and returns its expected identifying claim. Stdlib only. Exits non-zero on failure.
+"""
+import base64, json, sys, urllib.error, urllib.parse, urllib.request
+
+BASE = "http://localhost:8180"
+CLIENT = "big-portal"
+PWD = "test123"
+
+# realm, user, claim ("__roles__" => check realm_access.roles), expected-contains
+CHECKS = [
+    ("digid", "jan-burger", "bsn", "123456782"),
+    ("eherkenning", "acme-ondernemer", "kvk", "12345678"),
+    ("eidas", "pierre-dupont", "eidas_id", "FR/NL"),
+    ("medewerker", "merel-behandelaar", "__roles__", "behandelaar"),
+]
+
+
+def decode(jwt):
+    p = jwt.split(".")[1]
+    p += "=" * (-len(p) % 4)
+    return json.loads(base64.urlsafe_b64decode(p))
+
+
+def grant(realm, user):
+    data = urllib.parse.urlencode({
+        "grant_type": "password", "client_id": CLIENT,
+        "username": user, "password": PWD, "scope": "openid",
+    }).encode()
+    req = urllib.request.Request(
+        f"{BASE}/realms/{realm}/protocol/openid-connect/token", data=data,
+        headers={"Content-Type": "application/x-www-form-urlencoded"})
+    with urllib.request.urlopen(req, timeout=20) as r:
+        return json.loads(r.read())
+
+
+def main():
+    ok = True
+    for realm, user, claim, expect in CHECKS:
+        try:
+            at = decode(grant(realm, user)["access_token"])
+            if claim == "__roles__":
+                val = at.get("realm_access", {}).get("roles", [])
+                good = expect in val
+            else:
+                val = at.get(claim)
+                good = val is not None and expect in str(val)
+            print(f"{realm:12} {user:18} login OK | {claim} = {val} "
+                  f"[{'OK' if good else 'UNEXPECTED'}]")
+            ok = ok and good
+        except urllib.error.HTTPError as e:
+            ok = False
+            print(f"{realm:12} {user:18} LOGIN FAILED {e.code}: {e.read()[:200]!r}")
+    print("keycloak smoke OK" if ok else "keycloak smoke FAILED")
+    sys.exit(0 if ok else 1)
+
+
+if __name__ == "__main__":
+    main()

infra/keycloak/docker-compose.yml

@@ -0,0 +1,29 @@
+# Keycloak (S-02) with four pre-seeded realms imported at boot:
+#   digid · eherkenning · eidas · medewerker
+# Dev mode, H2 in-memory store, realm JSONs imported from ./realms.
+#
+#   docker compose -f infra/keycloak/docker-compose.yml up -d
+#   curl -s -o /dev/null -w '%{http_code}\n' \
+#     http://localhost:8180/realms/digid/.well-known/openid-configuration   # -> 200
+#
+# Admin console: http://localhost:8180/  (admin / admin — dev only)
+services:
+  keycloak:
+    image: quay.io/keycloak/keycloak:26.1
+    command: ["start-dev", "--import-realm"]
+    environment:
+      KC_BOOTSTRAP_ADMIN_USERNAME: admin
+      KC_BOOTSTRAP_ADMIN_PASSWORD: admin
+      # Older var names too, harmless on 26.x:
+      KEYCLOAK_ADMIN: admin
+      KEYCLOAK_ADMIN_PASSWORD: admin
+      KC_HEALTH_ENABLED: "true"
+      KC_HTTP_ENABLED: "true"
+    ports:
+      - "8180:8080"
+    volumes:
+      - ./realms:/opt/keycloak/data/import:ro,z
+    networks: [cg]
+
+networks:
+  cg:

infra/keycloak/realms/digid-realm.json

@@ -0,0 +1,43 @@
+{
+  "realm": "digid",
+  "enabled": true,
+  "displayName": "Mock DigiD",
+  "clients": [
+    {
+      "clientId": "big-portal",
+      "enabled": true,
+      "publicClient": true,
+      "standardFlowEnabled": true,
+      "directAccessGrantsEnabled": true,
+      "redirectUris": ["*"],
+      "webOrigins": ["*"],
+      "protocolMappers": [
+        {
+          "name": "bsn",
+          "protocol": "openid-connect",
+          "protocolMapper": "oidc-usermodel-attribute-mapper",
+          "config": {
+            "user.attribute": "bsn",
+            "claim.name": "bsn",
+            "jsonType.label": "String",
+            "id.token.claim": "true",
+            "access.token.claim": "true",
+            "userinfo.token.claim": "true"
+          }
+        }
+      ]
+    }
+  ],
+  "users": [
+    {
+      "username": "jan-burger",
+      "enabled": true,
+      "firstName": "Jan",
+      "lastName": "Burger",
+      "email": "jan.burger@example.nl",
+      "emailVerified": true,
+      "credentials": [{ "type": "password", "value": "test123", "temporary": false }],
+      "attributes": { "bsn": ["123456782"] }
+    }
+  ]
+}

infra/keycloak/realms/eherkenning-realm.json

@@ -0,0 +1,43 @@
+{
+  "realm": "eherkenning",
+  "enabled": true,
+  "displayName": "Mock eHerkenning",
+  "clients": [
+    {
+      "clientId": "big-portal",
+      "enabled": true,
+      "publicClient": true,
+      "standardFlowEnabled": true,
+      "directAccessGrantsEnabled": true,
+      "redirectUris": ["*"],
+      "webOrigins": ["*"],
+      "protocolMappers": [
+        {
+          "name": "kvk",
+          "protocol": "openid-connect",
+          "protocolMapper": "oidc-usermodel-attribute-mapper",
+          "config": {
+            "user.attribute": "kvk",
+            "claim.name": "kvk",
+            "jsonType.label": "String",
+            "id.token.claim": "true",
+            "access.token.claim": "true",
+            "userinfo.token.claim": "true"
+          }
+        }
+      ]
+    }
+  ],
+  "users": [
+    {
+      "username": "acme-ondernemer",
+      "enabled": true,
+      "firstName": "Anita",
+      "lastName": "Ondernemer",
+      "email": "anita@acme.nl",
+      "emailVerified": true,
+      "credentials": [{ "type": "password", "value": "test123", "temporary": false }],
+      "attributes": { "kvk": ["12345678"] }
+    }
+  ]
+}

infra/keycloak/realms/eidas-realm.json

@@ -0,0 +1,43 @@
+{
+  "realm": "eidas",
+  "enabled": true,
+  "displayName": "Mock eIDAS",
+  "clients": [
+    {
+      "clientId": "big-portal",
+      "enabled": true,
+      "publicClient": true,
+      "standardFlowEnabled": true,
+      "directAccessGrantsEnabled": true,
+      "redirectUris": ["*"],
+      "webOrigins": ["*"],
+      "protocolMappers": [
+        {
+          "name": "eidas_id",
+          "protocol": "openid-connect",
+          "protocolMapper": "oidc-usermodel-attribute-mapper",
+          "config": {
+            "user.attribute": "eidas_id",
+            "claim.name": "eidas_id",
+            "jsonType.label": "String",
+            "id.token.claim": "true",
+            "access.token.claim": "true",
+            "userinfo.token.claim": "true"
+          }
+        }
+      ]
+    }
+  ],
+  "users": [
+    {
+      "username": "pierre-dupont",
+      "enabled": true,
+      "firstName": "Pierre",
+      "lastName": "Dupont",
+      "email": "pierre.dupont@example.fr",
+      "emailVerified": true,
+      "credentials": [{ "type": "password", "value": "test123", "temporary": false }],
+      "attributes": { "eidas_id": ["FR/NL/AB-1234-5678"] }
+    }
+  ]
+}

infra/keycloak/realms/medewerker-realm.json

@@ -0,0 +1,44 @@
+{
+  "realm": "medewerker",
+  "enabled": true,
+  "displayName": "Medewerkers",
+  "roles": {
+    "realm": [
+      { "name": "behandelaar", "description": "Behandelt registratieaanvragen" },
+      { "name": "teamlead", "description": "Teamleider behandeling" }
+    ]
+  },
+  "clients": [
+    {
+      "clientId": "big-portal",
+      "enabled": true,
+      "publicClient": true,
+      "standardFlowEnabled": true,
+      "directAccessGrantsEnabled": true,
+      "redirectUris": ["*"],
+      "webOrigins": ["*"]
+    }
+  ],
+  "users": [
+    {
+      "username": "merel-behandelaar",
+      "enabled": true,
+      "firstName": "Merel",
+      "lastName": "Behandelaar",
+      "email": "merel@big.example.nl",
+      "emailVerified": true,
+      "credentials": [{ "type": "password", "value": "test123", "temporary": false }],
+      "realmRoles": ["behandelaar"]
+    },
+    {
+      "username": "tom-teamlead",
+      "enabled": true,
+      "firstName": "Tom",
+      "lastName": "Teamlead",
+      "email": "tom@big.example.nl",
+      "emailVerified": true,
+      "credentials": [{ "type": "password", "value": "test123", "temporary": false }],
+      "realmRoles": ["behandelaar", "teamlead"]
+    }
+  ]
+}

infra/opennotificaties/docker-compose.yml

@@ -0,0 +1,91 @@
+# Open Notificaties (NRC) stack (S-01-c). Lean adaptation of the upstream dev compose:
+# db (PostGIS) + redis (also the Celery broker) + migrate-init + the API + a celery worker.
+#
+# Shares the `cg` network with the OpenZaak stack so the two can reach each other.
+# Run BOTH together (NRC needs OpenZaak's Autorisaties API for auth wiring):
+#
+#   docker compose -f infra/openzaak/docker-compose.yml -f infra/opennotificaties/docker-compose.yml up -d
+#   curl -s -o /dev/null -w '%{http_code}\n' http://localhost:8001/admin/   # -> 302
+#
+# NRC is published on host :8001 (OpenZaak holds :8000).
+services:
+  nrc-db:
+    image: docker.io/postgis/postgis:17-3.5
+    environment:
+      POSTGRES_USER: opennotificaties
+      POSTGRES_PASSWORD: opennotificaties
+      POSTGRES_DB: opennotificaties
+    command: postgres -c max_connections=300
+    volumes:
+      - nrc-db:/var/lib/postgresql/data
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U opennotificaties -d opennotificaties"]
+      interval: 5s
+      timeout: 3s
+      retries: 10
+    networks: [cg]
+
+  nrc-redis:
+    image: docker.io/library/redis:7
+    networks: [cg]
+
+  nrc-init:
+    image: docker.io/openzaak/open-notificaties:${OPENNOTIFICATIES_TAG:-latest}
+    environment: &nrc-env
+      DJANGO_SETTINGS_MODULE: nrc.conf.docker
+      SECRET_KEY: ${NRC_SECRET_KEY:-dev-only-not-for-production}
+      DB_HOST: nrc-db
+      DB_NAME: opennotificaties
+      DB_USER: opennotificaties
+      DB_PASSWORD: opennotificaties
+      IS_HTTPS: "no"
+      ALLOWED_HOSTS: "*"
+      CACHE_DEFAULT: nrc-redis:6379/0
+      CACHE_AXES: nrc-redis:6379/0
+      CELERY_BROKER_URL: redis://nrc-redis:6379/1
+      CELERY_RESULT_BACKEND: redis://nrc-redis:6379/1
+      DISABLE_2FA: "true"
+      OPENNOTIFICATIES_SUPERUSER_USERNAME: admin
+      DJANGO_SUPERUSER_PASSWORD: admin
+      OPENNOTIFICATIES_SUPERUSER_EMAIL: admin@localhost
+      RUN_SETUP_CONFIG: "true"
+    command: /setup_configuration.sh
+    volumes:
+      - ./setup_configuration:/app/setup_configuration:ro,z
+    depends_on:
+      nrc-db:
+        condition: service_healthy
+      nrc-redis:
+        condition: service_started
+    networks: [cg]
+
+  nrc-web:
+    image: docker.io/openzaak/open-notificaties:${OPENNOTIFICATIES_TAG:-latest}
+    environment: *nrc-env
+    healthcheck:
+      test: ["CMD", "python", "-c", "import requests,sys; sys.exit(0 if requests.head('http://localhost:8000/admin/').status_code in (200,302) else 1)"]
+      interval: 10s
+      timeout: 5s
+      retries: 10
+      start_period: 30s
+    ports:
+      - "8001:8000"
+    depends_on:
+      nrc-init:
+        condition: service_completed_successfully
+    networks: [cg]
+
+  nrc-celery:
+    image: docker.io/openzaak/open-notificaties:${OPENNOTIFICATIES_TAG:-latest}
+    environment: *nrc-env
+    command: /celery_worker.sh
+    depends_on:
+      nrc-init:
+        condition: service_completed_successfully
+    networks: [cg]
+
+volumes:
+  nrc-db:
+
+networks:
+  cg:

infra/opennotificaties/setup_configuration/data.yaml

@@ -0,0 +1,5 @@
+# Open Notificaties setup_configuration.
+# Stage 1 (this commit): intentionally minimal — the init container runs
+# migrations; no steps enabled yet. The OpenZaak<->NRC notification wiring
+# (Services, Authorization, JWT, Kanalen) is added next. See ADR-0002 / S-01-c.
+{}

infra/openzaak/docker-compose.yml

@@ -22,11 +22,11 @@ services:
       interval: 5s
       timeout: 3s
       retries: 10
-    networks: [oz]
+    networks: [cg]
 
   oz-redis:
     image: docker.io/library/redis:7
-    networks: [oz]
+    networks: [cg]
 
   oz-init:
     image: docker.io/openzaak/open-zaak:${OPENZAAK_TAG:-latest}
@@ -61,7 +61,7 @@ services:
         condition: service_healthy
       oz-redis:
         condition: service_started
-    networks: [oz]
+    networks: [cg]
 
   openzaak:
     image: docker.io/openzaak/open-zaak:${OPENZAAK_TAG:-latest}
@@ -77,7 +77,7 @@ services:
     depends_on:
       oz-init:
         condition: service_completed_successfully
-    networks: [oz]
+    networks: [cg]
 
   oz-celery:
     image: docker.io/openzaak/open-zaak:${OPENZAAK_TAG:-latest}
@@ -86,10 +86,10 @@ services:
     depends_on:
       oz-init:
         condition: service_completed_successfully
-    networks: [oz]
+    networks: [cg]
 
 volumes:
   oz-db:
 
 networks:
-  oz:
+  cg:

mkdocs.yml

@@ -23,6 +23,9 @@ nav:
   - Product Requirements: PRD.md
   - Architecture:
       - "ADR-0001: Loose coupling": architecture/adr-0001-loose-coupling.md
+      - "ADR-0002: Catalogus design": architecture/adr-0002-catalogus-design.md
+      - "ADR-0003: ACL default-fill": architecture/adr-0003-default-fill.md
+      - "ADR-0004: BDD framework": architecture/adr-0004-bdd-framework.md
   - Working in Gitea: gitea-workflow.md
   - Runbooks:
       - CI: runbooks/ci.md

register-referentie.slnx

@@ -0,0 +1,16 @@
+<Solution>
+  <Folder Name="/services/" />
+  <Folder Name="/services/acl/">
+    <Project Path="services/acl/Acl.Api/Acl.Api.csproj" />
+    <Project Path="services/acl/Acl.Application/Acl.Application.csproj" />
+    <Project Path="services/acl/Acl.Infrastructure/Acl.Infrastructure.csproj" />
+    <Project Path="services/acl/Acl.Tests/Acl.Tests.csproj" />
+  </Folder>
+  <Folder Name="/services/bff/">
+    <Project Path="services/bff/Bff.Api/Bff.Api.csproj" />
+    <Project Path="services/bff/Bff.Tests/Bff.Tests.csproj" />
+  </Folder>
+  <Folder Name="/tests/">
+    <Project Path="tests/acceptance/Acceptance.csproj" />
+  </Folder>
+</Solution>

services/acl/Acl.Api/Acl.Api.csproj

@@ -0,0 +1,14 @@
+<Project Sdk="Microsoft.NET.Sdk.Web">
+
+  <ItemGroup>
+    <ProjectReference Include="..\Acl.Application\Acl.Application.csproj" />
+    <ProjectReference Include="..\Acl.Infrastructure\Acl.Infrastructure.csproj" />
+  </ItemGroup>
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+  </PropertyGroup>
+
+</Project>

services/acl/Acl.Api/Program.cs

@@ -0,0 +1,31 @@
+using Acl.Application;
+using Acl.Infrastructure;
+
+var builder = WebApplication.CreateBuilder(args);
+
+builder.Services.AddSingleton<IClock, SystemClock>();
+builder.Services.AddSingleton(sp => sp.GetRequiredService<IConfiguration>()
+    .GetSection("Acl:Defaults").Get<AclDefaults>()
+    ?? throw new InvalidOperationException("Missing configuration section 'Acl:Defaults'"));
+builder.Services.AddSingleton(sp => sp.GetRequiredService<IConfiguration>()
+    .GetSection("Acl:OpenZaak").Get<OpenZaakOptions>()
+    ?? throw new InvalidOperationException("Missing configuration section 'Acl:OpenZaak'"));
+builder.Services.AddHttpClient<IZaakGateway, OpenZaakGateway>();
+builder.Services.AddScoped<AclService>();
+
+var app = builder.Build();
+
+app.MapGet("/health", () => "Healthy");
+
+// The ACL's single operation, exposed as a service endpoint.
+app.MapPost("/zaken", async (OpenZaakRequest body, AclService acl, CancellationToken ct) =>
+{
+    var zaakUrl = await acl.OpenZaakAsync(new DomainRegistration(body.Bsn), ct);
+    return Results.Ok(new { zaakUrl = zaakUrl.ToString() });
+});
+
+app.Run();
+
+public sealed record OpenZaakRequest(string Bsn);
+
+public partial class Program;

services/acl/Acl.Api/Properties/launchSettings.json

@@ -0,0 +1,23 @@
+{
+  "$schema": "https://json.schemastore.org/launchsettings.json",
+  "profiles": {
+    "http": {
+      "commandName": "Project",
+      "dotnetRunMessages": true,
+      "launchBrowser": true,
+      "applicationUrl": "http://localhost:5041",
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development"
+      }
+    },
+    "https": {
+      "commandName": "Project",
+      "dotnetRunMessages": true,
+      "launchBrowser": true,
+      "applicationUrl": "https://localhost:7260;http://localhost:5041",
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development"
+      }
+    }
+  }
+}

services/acl/Acl.Api/appsettings.Development.json

@@ -0,0 +1,8 @@
+{
+  "Logging": {
+    "LogLevel": {
+      "Default": "Information",
+      "Microsoft.AspNetCore": "Warning"
+    }
+  }
+}

services/acl/Acl.Api/appsettings.json

@@ -0,0 +1,9 @@
+{
+  "Logging": {
+    "LogLevel": {
+      "Default": "Information",
+      "Microsoft.AspNetCore": "Warning"
+    }
+  },
+  "AllowedHosts": "*"
+}

services/acl/Acl.Application/Acl.Application.csproj

@@ -0,0 +1,9 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

services/acl/Acl.Application/AclDefaults.cs

@@ -0,0 +1,10 @@
+namespace Acl.Application;
+
+/// <summary>Configured ZGW defaults the ACL fills in (ADR-0003).</summary>
+public sealed class AclDefaults
+{
+    public required string Bronorganisatie { get; init; }
+    public required string VerantwoordelijkeOrganisatie { get; init; }
+    public required string Vertrouwelijkheidaanduiding { get; init; }
+    public required Uri ZaaktypeUrl { get; init; }
+}

services/acl/Acl.Application/AclService.cs

@@ -0,0 +1,20 @@
+namespace Acl.Application;
+
+/// <summary>The ACL's single operation: open a zaak from a domain payload,
+/// default-filling the ZGW-mandatory fields (ADR-0003).</summary>
+public sealed class AclService(IZaakGateway gateway, AclDefaults defaults, IClock clock)
+{
+    public Task<Uri> OpenZaakAsync(DomainRegistration registration, CancellationToken ct = default)
+    {
+        ArgumentNullException.ThrowIfNull(registration);
+
+        var request = new ZaakRequest(
+            defaults.Bronorganisatie,
+            defaults.VerantwoordelijkeOrganisatie,
+            defaults.Vertrouwelijkheidaanduiding,
+            defaults.ZaaktypeUrl,
+            clock.Today);
+
+        return gateway.OpenZaakAsync(request, ct);
+    }
+}

services/acl/Acl.Application/DomainRegistration.cs

@@ -0,0 +1,4 @@
+namespace Acl.Application;
+
+/// <summary>Domain-language payload handed to the ACL. No ZGW concepts here.</summary>
+public sealed record DomainRegistration(string Bsn);

services/acl/Acl.Application/IClock.cs

@@ -0,0 +1,7 @@
+namespace Acl.Application;
+
+/// <summary>Abstracts "today" so startdatum default-fill is deterministic in tests.</summary>
+public interface IClock
+{
+    DateOnly Today { get; }
+}

services/acl/Acl.Application/IZaakGateway.cs

@@ -0,0 +1,8 @@
+namespace Acl.Application;
+
+/// <summary>Port to the ZGW Zaken API. Implemented in Infrastructure — the only
+/// code that talks to OpenZaak (ADR-0001).</summary>
+public interface IZaakGateway
+{
+    Task<Uri> OpenZaakAsync(ZaakRequest request, CancellationToken ct = default);
+}

services/acl/Acl.Application/ZaakRequest.cs

@@ -0,0 +1,9 @@
+namespace Acl.Application;
+
+/// <summary>The fully default-filled zaak the gateway will create in OpenZaak.</summary>
+public sealed record ZaakRequest(
+    string Bronorganisatie,
+    string VerantwoordelijkeOrganisatie,
+    string Vertrouwelijkheidaanduiding,
+    Uri Zaaktype,
+    DateOnly Startdatum);

services/acl/Acl.Infrastructure/Acl.Infrastructure.csproj

@@ -0,0 +1,13 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <ItemGroup>
+    <ProjectReference Include="..\Acl.Application\Acl.Application.csproj" />
+  </ItemGroup>
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

services/acl/Acl.Infrastructure/OpenZaakGateway.cs

@@ -0,0 +1,48 @@
+using System.Net.Http.Headers;
+using System.Net.Http.Json;
+using System.Text.Json.Serialization;
+using Acl.Application;
+
+namespace Acl.Infrastructure;
+
+/// <summary>The only code that talks to OpenZaak's Zaken API (ADR-0001).</summary>
+public sealed class OpenZaakGateway(HttpClient http, OpenZaakOptions options) : IZaakGateway
+{
+    public async Task<Uri> OpenZaakAsync(ZaakRequest request, CancellationToken ct = default)
+    {
+        ArgumentNullException.ThrowIfNull(request);
+
+        using var message = new HttpRequestMessage(
+            HttpMethod.Post, new Uri(options.BaseUrl, "/zaken/api/v1/zaken"))
+        {
+            Content = JsonContent.Create(new ZaakDto(
+                request.Bronorganisatie,
+                request.Zaaktype.ToString(),
+                request.VerantwoordelijkeOrganisatie,
+                request.Startdatum.ToString("yyyy-MM-dd"),
+                request.Vertrouwelijkheidaanduiding)),
+        };
+        message.Headers.Authorization =
+            new AuthenticationHeaderValue("Bearer", ZgwToken.Mint(options.ClientId, options.Secret));
+        // ZRC is a geo API; it requires the CRS headers.
+        message.Headers.Add("Accept-Crs", "EPSG:4326");
+        message.Content.Headers.Add("Content-Crs", "EPSG:4326");
+
+        using var response = await http.SendAsync(message, ct);
+        response.EnsureSuccessStatusCode();
+
+        var created = await response.Content.ReadFromJsonAsync<ZaakCreatedDto>(ct)
+            ?? throw new InvalidOperationException("OpenZaak returned an empty zaak response");
+        return new Uri(created.Url);
+    }
+
+    private sealed record ZaakDto(
+        [property: JsonPropertyName("bronorganisatie")] string Bronorganisatie,
+        [property: JsonPropertyName("zaaktype")] string Zaaktype,
+        [property: JsonPropertyName("verantwoordelijkeOrganisatie")] string VerantwoordelijkeOrganisatie,
+        [property: JsonPropertyName("startdatum")] string Startdatum,
+        [property: JsonPropertyName("vertrouwelijkheidaanduiding")] string Vertrouwelijkheidaanduiding);
+
+    private sealed record ZaakCreatedDto(
+        [property: JsonPropertyName("url")] string Url);
+}

services/acl/Acl.Infrastructure/OpenZaakOptions.cs

@@ -0,0 +1,9 @@
+namespace Acl.Infrastructure;
+
+/// <summary>Connection + credential config for OpenZaak's ZGW APIs.</summary>
+public sealed class OpenZaakOptions
+{
+    public required Uri BaseUrl { get; init; }
+    public required string ClientId { get; init; }
+    public required string Secret { get; init; }
+}

services/acl/Acl.Infrastructure/SystemClock.cs

@@ -0,0 +1,8 @@
+using Acl.Application;
+
+namespace Acl.Infrastructure;
+
+public sealed class SystemClock : IClock
+{
+    public DateOnly Today => DateOnly.FromDateTime(DateTime.UtcNow);
+}

services/acl/Acl.Infrastructure/ZgwToken.cs

@@ -0,0 +1,29 @@
+using System.Security.Cryptography;
+using System.Text;
+using System.Text.Json;
+
+namespace Acl.Infrastructure;
+
+/// <summary>Mints a ZGW (vng-api-common) JWT: HS256 over the standard claims.</summary>
+internal static class ZgwToken
+{
+    public static string Mint(string clientId, string secret)
+    {
+        var header = B64Url(JsonSerializer.SerializeToUtf8Bytes(new { alg = "HS256", typ = "JWT" }));
+        var payload = B64Url(JsonSerializer.SerializeToUtf8Bytes(new
+        {
+            iss = clientId,
+            iat = DateTimeOffset.UtcNow.ToUnixTimeSeconds(),
+            client_id = clientId,
+            user_id = "acl",
+            user_representation = "acl",
+        }));
+        var signingInput = $"{header}.{payload}";
+        using var hmac = new HMACSHA256(Encoding.UTF8.GetBytes(secret));
+        var signature = B64Url(hmac.ComputeHash(Encoding.UTF8.GetBytes(signingInput)));
+        return $"{signingInput}.{signature}";
+    }
+
+    private static string B64Url(byte[] bytes) =>
+        Convert.ToBase64String(bytes).TrimEnd('=').Replace('+', '-').Replace('/', '_');
+}

services/acl/Acl.Tests/Acl.Tests.csproj

@@ -0,0 +1,26 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="coverlet.collector" Version="6.0.4" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.14.1" />
+    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="3.1.4" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <Using Include="Xunit" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Acl.Application\Acl.Application.csproj" />
+    <ProjectReference Include="..\Acl.Infrastructure\Acl.Infrastructure.csproj" />
+  </ItemGroup>
+
+</Project>

services/acl/Acl.Tests/AclServiceTests.cs

@@ -0,0 +1,47 @@
+using Acl.Application;
+
+namespace Acl.Tests;
+
+public class AclServiceTests
+{
+    private sealed class FakeGateway : IZaakGateway
+    {
+        public ZaakRequest? Captured;
+        public Uri Result { get; } = new("http://openzaak/zaken/api/v1/zaken/abc");
+
+        public Task<Uri> OpenZaakAsync(ZaakRequest request, CancellationToken ct = default)
+        {
+            Captured = request;
+            return Task.FromResult(Result);
+        }
+    }
+
+    private sealed class FixedClock(DateOnly today) : IClock
+    {
+        public DateOnly Today { get; } = today;
+    }
+
+    [Fact]
+    public async Task Opening_a_zaak_default_fills_zgw_fields_and_returns_the_zaak_url()
+    {
+        var gateway = new FakeGateway();
+        var defaults = new AclDefaults
+        {
+            Bronorganisatie = "517439943",
+            VerantwoordelijkeOrganisatie = "517439943",
+            Vertrouwelijkheidaanduiding = "openbaar",
+            ZaaktypeUrl = new("http://openzaak/catalogi/api/v1/zaaktypen/big"),
+        };
+        var service = new AclService(gateway, defaults, new FixedClock(new DateOnly(2026, 6, 4)));
+
+        var url = await service.OpenZaakAsync(new DomainRegistration("123456782"));
+
+        Assert.Equal(gateway.Result, url);
+        var req = Assert.IsType<ZaakRequest>(gateway.Captured);
+        Assert.Equal("517439943", req.Bronorganisatie);
+        Assert.Equal("517439943", req.VerantwoordelijkeOrganisatie);
+        Assert.Equal("openbaar", req.Vertrouwelijkheidaanduiding);
+        Assert.Equal(defaults.ZaaktypeUrl, req.Zaaktype);
+        Assert.Equal(new DateOnly(2026, 6, 4), req.Startdatum);
+    }
+}

services/acl/Acl.Tests/OpenZaakGatewayTests.cs

@@ -0,0 +1,51 @@
+using System.Net;
+using System.Net.Http.Json;
+using Acl.Application;
+using Acl.Infrastructure;
+
+namespace Acl.Tests;
+
+public class OpenZaakGatewayTests
+{
+    private sealed class StubHandler(Func<HttpRequestMessage, Task<HttpResponseMessage>> onSend)
+        : HttpMessageHandler
+    {
+        protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken ct)
+            => onSend(request);
+    }
+
+    [Fact]
+    public async Task Posts_zaak_to_openzaak_with_bearer_and_default_fields_and_returns_url()
+    {
+        HttpRequestMessage? seen = null;
+        string? body = null;
+        var handler = new StubHandler(async req =>
+        {
+            seen = req;
+            body = await req.Content!.ReadAsStringAsync();
+            return new HttpResponseMessage(HttpStatusCode.Created)
+            {
+                Content = JsonContent.Create(new { url = "http://openzaak/zaken/api/v1/zaken/xyz" }),
+            };
+        });
+        var gateway = new OpenZaakGateway(
+            new HttpClient(handler),
+            new OpenZaakOptions { BaseUrl = new("http://openzaak"), ClientId = "cid", Secret = "sec" });
+        var request = new ZaakRequest(
+            "517439943", "517439943", "openbaar",
+            new("http://openzaak/catalogi/api/v1/zaaktypen/big"), new DateOnly(2026, 6, 4));
+
+        var url = await gateway.OpenZaakAsync(request);
+
+        Assert.Equal("http://openzaak/zaken/api/v1/zaken/xyz", url.ToString());
+        Assert.Equal(HttpMethod.Post, seen!.Method);
+        Assert.Equal("http://openzaak/zaken/api/v1/zaken", seen.RequestUri!.ToString());
+        Assert.Equal("Bearer", seen.Headers.Authorization!.Scheme);
+        Assert.False(string.IsNullOrWhiteSpace(seen.Headers.Authorization.Parameter));
+        Assert.Contains("\"bronorganisatie\":\"517439943\"", body);
+        Assert.Contains("\"verantwoordelijkeOrganisatie\":\"517439943\"", body);
+        Assert.Contains("\"vertrouwelijkheidaanduiding\":\"openbaar\"", body);
+        Assert.Contains("\"startdatum\":\"2026-06-04\"", body);
+        Assert.Contains("\"zaaktype\":\"http://openzaak/catalogi/api/v1/zaaktypen/big\"", body);
+    }
+}

services/acl/Acl.slnx

@@ -0,0 +1,6 @@
+<Solution>
+  <Project Path="Acl.Api/Acl.Api.csproj" />
+  <Project Path="Acl.Application/Acl.Application.csproj" />
+  <Project Path="Acl.Infrastructure/Acl.Infrastructure.csproj" />
+  <Project Path="Acl.Tests/Acl.Tests.csproj" />
+</Solution>

tests/acceptance/Acceptance.csproj

@@ -0,0 +1,23 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="coverlet.collector" Version="6.0.4" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.14.1" />
+    <PackageReference Include="Reqnroll.xUnit" Version="3.3.4" />
+    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="3.1.4" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\services\acl\Acl.Application\Acl.Application.csproj" />
+    <ProjectReference Include="..\..\services\acl\Acl.Infrastructure\Acl.Infrastructure.csproj" />
+  </ItemGroup>
+
+</Project>

tests/acceptance/Features/EenZaakOpenen.feature

@@ -0,0 +1,27 @@
+# language: en
+# Drives S-04 (#5). The ACL is the only code that talks to ZGW (ADR-0001); it
+# default-fills the ZGW-mandatory zaak fields the domain never sees (ADR-0003).
+# Real-OpenZaak verification is a separate slice — this scenario exercises the
+# use case against an in-memory stand-in for the Zaken API.
+Feature: Een zaak openen vanuit een registratie
+  Als domein wil ik de ACL vragen een zaak te openen
+  zodat de ZGW-verplichte velden worden ingevuld zonder dat het domein ze kent.
+
+  Scenario: De ACL vult de ZGW-verplichte velden default in
+    Given a domain registration for BSN "123456782"
+    And the ACL is configured with these defaults:
+      | field                        | value                                         |
+      | bronorganisatie              | 517439943                                     |
+      | verantwoordelijkeOrganisatie | 517439943                                     |
+      | vertrouwelijkheidaanduiding  | openbaar                                      |
+      | zaaktype                     | http://openzaak/catalogi/api/v1/zaaktypen/big |
+    And today is "2026-06-04"
+    When the domain asks the ACL to open a zaak
+    Then a zaak is created with these default-filled fields
+      | field                        | value                                         |
+      | bronorganisatie              | 517439943                                     |
+      | verantwoordelijkeOrganisatie | 517439943                                     |
+      | vertrouwelijkheidaanduiding  | openbaar                                      |
+      | zaaktype                     | http://openzaak/catalogi/api/v1/zaaktypen/big |
+      | startdatum                   | 2026-06-04                                    |
+    And the ACL returns the URL of the created zaak

tests/acceptance/Steps/EenZaakOpenenSteps.cs

@@ -0,0 +1,65 @@
+using Acceptance.Support;
+using Acl.Application;
+using Reqnroll;
+using Xunit;
+
+namespace Acceptance.Steps;
+
+/// <summary>Bindings for <c>EenZaakOpenen.feature</c>. Reqnroll creates one
+/// instance per scenario, so instance fields hold scenario-scoped state.</summary>
+[Binding]
+public sealed class EenZaakOpenenSteps
+{
+    private readonly InMemoryZaakGateway _gateway = new();
+    private DomainRegistration? _registration;
+    private AclDefaults? _defaults;
+    private DateOnly _today;
+    private Uri? _returnedUrl;
+
+    [Given("a domain registration for BSN \"(.*)\"")]
+    public void GivenADomainRegistrationForBsn(string bsn)
+        => _registration = new DomainRegistration(bsn);
+
+    [Given("the ACL is configured with these defaults:")]
+    public void GivenTheAclIsConfiguredWithTheseDefaults(DataTable defaults)
+    {
+        var values = ToFieldMap(defaults);
+        _defaults = new AclDefaults
+        {
+            Bronorganisatie = values["bronorganisatie"],
+            VerantwoordelijkeOrganisatie = values["verantwoordelijkeOrganisatie"],
+            Vertrouwelijkheidaanduiding = values["vertrouwelijkheidaanduiding"],
+            ZaaktypeUrl = new Uri(values["zaaktype"]),
+        };
+    }
+
+    [Given("today is \"(.*)\"")]
+    public void GivenTodayIs(string date)
+        => _today = DateOnly.Parse(date);
+
+    [When("the domain asks the ACL to open a zaak")]
+    public async Task WhenTheDomainAsksTheAclToOpenAZaak()
+    {
+        var service = new AclService(_gateway, _defaults!, new FixedClock(_today));
+        _returnedUrl = await service.OpenZaakAsync(_registration!);
+    }
+
+    [Then("a zaak is created with these default-filled fields")]
+    public void ThenAZaakIsCreatedWithTheseDefaultFilledFields(DataTable expected)
+    {
+        var request = Assert.IsType<ZaakRequest>(_gateway.Captured);
+        var fields = ToFieldMap(expected);
+        Assert.Equal(fields["bronorganisatie"], request.Bronorganisatie);
+        Assert.Equal(fields["verantwoordelijkeOrganisatie"], request.VerantwoordelijkeOrganisatie);
+        Assert.Equal(fields["vertrouwelijkheidaanduiding"], request.Vertrouwelijkheidaanduiding);
+        Assert.Equal(fields["zaaktype"], request.Zaaktype.ToString());
+        Assert.Equal(fields["startdatum"], request.Startdatum.ToString("yyyy-MM-dd"));
+    }
+
+    [Then("the ACL returns the URL of the created zaak")]
+    public void ThenTheAclReturnsTheUrlOfTheCreatedZaak()
+        => Assert.Equal(InMemoryZaakGateway.CreatedZaakUrl, _returnedUrl);
+
+    private static Dictionary<string, string> ToFieldMap(DataTable table)
+        => table.Rows.ToDictionary(r => r["field"], r => r["value"]);
+}

tests/acceptance/Support/FixedClock.cs

@@ -0,0 +1,10 @@
+using Acl.Application;
+
+namespace Acceptance.Support;
+
+/// <summary>A clock pinned to a known date so <c>startdatum</c> is deterministic
+/// in scenarios (ADR-0003).</summary>
+public sealed class FixedClock(DateOnly today) : IClock
+{
+    public DateOnly Today { get; } = today;
+}

tests/acceptance/Support/InMemoryZaakGateway.cs

@@ -0,0 +1,20 @@
+using Acl.Application;
+
+namespace Acceptance.Support;
+
+/// <summary>An in-memory stand-in for the OpenZaak Zaken API. It captures the
+/// fully default-filled <see cref="ZaakRequest"/> the ACL builds and returns a
+/// fixed zaak URL, so the acceptance scenario can verify the use case without a
+/// running OpenZaak (real-OpenZaak verification is a separate slice).</summary>
+public sealed class InMemoryZaakGateway : IZaakGateway
+{
+    public static readonly Uri CreatedZaakUrl = new("http://openzaak/zaken/api/v1/zaken/created-123");
+
+    public ZaakRequest? Captured { get; private set; }
+
+    public Task<Uri> OpenZaakAsync(ZaakRequest request, CancellationToken ct = default)
+    {
+        Captured = request;
+        return Task.FromResult(CreatedZaakUrl);
+    }
+}

workflows/registratie.bpmn

@@ -0,0 +1,48 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<definitions xmlns="http://www.omg.org/spec/BPMN/20100524/MODEL"
+             xmlns:flowable="http://flowable.org/bpmn"
+             xmlns:bpmndi="http://www.omg.org/spec/BPMN/20100524/DI"
+             xmlns:omgdc="http://www.omg.org/spec/DD/20100524/DC"
+             xmlns:omgdi="http://www.omg.org/spec/DD/20100524/DI"
+             targetNamespace="http://respellion.nl/big">
+
+  <!-- S-03: minimal "Registratie ontvangen" flow.
+       start -> external-worker task (OpenZaakAanmaken) -> end.
+       The external task is handled by the Workflow Client / ACL in later slices. -->
+  <process id="registratie" name="Registratie ontvangen" isExecutable="true">
+
+    <startEvent id="start" name="Registratie ontvangen"/>
+
+    <sequenceFlow id="flow1" sourceRef="start" targetRef="OpenZaakAanmaken"/>
+
+    <serviceTask id="OpenZaakAanmaken" name="OpenZaak aanmaken"
+                 flowable:type="external-worker"
+                 flowable:topic="OpenZaakAanmaken"/>
+
+    <sequenceFlow id="flow2" sourceRef="OpenZaakAanmaken" targetRef="end"/>
+
+    <endEvent id="end" name="Zaak aangemaakt"/>
+  </process>
+
+  <bpmndi:BPMNDiagram id="diagram">
+    <bpmndi:BPMNPlane id="plane" bpmnElement="registratie">
+      <bpmndi:BPMNShape id="s_start" bpmnElement="start">
+        <omgdc:Bounds x="100" y="100" width="30" height="30"/>
+      </bpmndi:BPMNShape>
+      <bpmndi:BPMNShape id="s_task" bpmnElement="OpenZaakAanmaken">
+        <omgdc:Bounds x="200" y="85" width="120" height="60"/>
+      </bpmndi:BPMNShape>
+      <bpmndi:BPMNShape id="s_end" bpmnElement="end">
+        <omgdc:Bounds x="400" y="100" width="30" height="30"/>
+      </bpmndi:BPMNShape>
+      <bpmndi:BPMNEdge id="e_flow1" bpmnElement="flow1">
+        <omgdi:waypoint x="130" y="115"/>
+        <omgdi:waypoint x="200" y="115"/>
+      </bpmndi:BPMNEdge>
+      <bpmndi:BPMNEdge id="e_flow2" bpmnElement="flow2">
+        <omgdi:waypoint x="320" y="115"/>
+        <omgdi:waypoint x="400" y="115"/>
+      </bpmndi:BPMNEdge>
+    </bpmndi:BPMNPlane>
+  </bpmndi:BPMNDiagram>
+</definitions>