atomic-design-poc/docs/project/backlog/WP-53-inbound-identity-and-citizen-scoping.md

# WP-53 — Inbound identity + citizen-scoping (the ZGW auth seam)

Status: todo
Phase: 9 — OpenZaak / ZGW integration

## Why

WP-49 made the cases read path swappable, but everything runs as a **stubbed identity**: the
principal comes from an `X-Role` header and the "owner" is a single hardcoded BSN. A real
OpenZaak integration needs a genuine per-request user in order to (a) fill the ZGW JWT
`user_id`/`user_representation` audit claims, and (b) **scope zaken to the logged-in citizen**
(you must never return another citizen's cases). This WP threads a real identity through the
system **without** building DigiD/OIDC itself — CLAUDE.md keeps real auth out of scope, so the
deliverable is the _seam_: a per-request `CallerIdentity` (subject BSN + display name) produced
by a **pluggable, stubbed** provider, consumed everywhere the hardcoded owner is used today.
Production later swaps the stub for OIDC/DigiD without touching any consumer.

## Context — current state (read before designing; this is the handoff, no prior chat needed)

Identity is faked in these exact places — this WP replaces the fakes with one identity flow:

- **Backend principal**: `backend/src/BigRegister.Api/Domain/Authorization/Authz.cs` —
  `ResolvePrincipal(ctx)` reads the `X-Role` header (drafter/approver/admin). Its own doc
  comment says _"A real system builds this from verified AD/OIDC claims … everything else in
  this file carries over unchanged once that swap happens."_ That is the seam to formalize.
- **Hardcoded owner/BSN**: `backend/src/BigRegister.Api/Data/DocumentStore.cs` —
  `public const string DemoOwner = "19012345601";` (the single seeded citizen's BIG-nummer).
  Grep `DemoOwner` across `Program.cs` + stores — every "whose data is this" decision uses it.
- **Owner-scoped stores** already take an `owner` string:
  `Data/ApplicationStore.cs` (`List(owner)`, `Get(id, owner)`, `CreateConcept(type, owner)`,
  `Submit(id, owner, …)`) and `Data/DocumentStore.cs`. They are ready to receive a real BSN —
  today the endpoints pass `DocumentStore.DemoOwner`.
- **ZGW JWT user claims** are static: `Zgw/ZgwTokenProvider.cs` `Mint()` reads
  `ZgwOptions.UserId` / `ZgwOptions.UserRepresentation` (constant strings). These must become
  **per-request** (the acting citizen), or the ZGW audit trail is wrong.
- **The cases read interface** `Data/IZaakSource.cs` has one method, `ListCases(now)`, with **no
  caller** — it returns the admin cross-owner list. There is no citizen-scoped "my cases" read
  yet, and `OpenZaakZaakSource` lists ALL zaken (`{ZrcBaseUrl}/zaken`, no filter).
- **Correlation middleware** (`Program.cs`, the `app.Use(...)` block setting
  `X-Correlation-Id`) is the pattern/location to add an identity-resolution middleware next to.
- **Frontend** identity is the dev role switch: `?role=drafter|approver|admin` + the `⚙ state`
  panel + `SessionStore` (`src/app/auth/`), documented in `docs/reference/roles-and-access.md`.
  The FE already persists a session (localStorage). No FE change is required for the backend
  seam, but the citizen's BSN must originate from the session, not a constant — note where.

ZGW detail that drives the scoping query: OpenZaak filters a citizen's zaken via the query
param `rol__betrokkeneIdentificatie__natuurlijkPersoon__inpBsn=<bsn>` on `GET {ZRC}/zaken`.

## Read first

- [openzaak-integration.md](../reference/openzaak-integration.md) — the seam + the "two nested
  ACLs" section (this WP is about the identity that flows through both).
- [ADR-0005 — OpenZaak behind the BFF](../reference/architecture/0005-openzaak-behind-bff.md)
  ("Deferred: real inbound OIDC/JWT auth" — this WP formalizes the seam, not the provider).
- [ADR-0002 — user groups & bounded contexts](../reference/architecture/0002-user-groups-and-bounded-contexts.md),
  [roles-and-access.md](../reference/roles-and-access.md).
- `CLAUDE.md` → "Out of scope: Real auth/DigiD" — respect it: build the seam + a stub, not DigiD.

## Decisions (pre-made, don't relitigate)

- **Seam, not provider.** Introduce a `CallerIdentity` (subject BSN + display name + role) and an
  `IIdentityProvider` with a **`StubIdentityProvider`** (reads the existing `X-Role` + a
  configurable/`X-Subject` BSN, defaulting to the seeded citizen). Production swaps the provider;
  no consumer changes. Do **not** add DigiD/OIDC.
- **One source of "who".** Resolve `CallerIdentity` once per request (middleware, beside the
  correlation block) and flow it to: `Authz.ResolvePrincipal`, the store `owner` arguments
  (replace `DocumentStore.DemoOwner` call sites), and `ZgwTokenProvider.Mint(caller)`.
- **Citizen-scoped reads are separate from admin reads.** Keep the admin cross-owner list
  (`cases:manage`) as-is; add a citizen-scoped "my zaken" path that filters by the caller's BSN
  (ZGW `rol__…__inpBsn`; local store: `List(owner)`).
- **Ownership stays server-authoritative.** The BSN comes from the resolved identity, never from
  a client-supplied body field.

## Files

- New: `Domain/Authorization/CallerIdentity.cs`, `Domain/Authorization/IIdentityProvider.cs` +
  `StubIdentityProvider.cs`; an identity-resolution middleware in `Program.cs`.
- Edit: `Domain/Authorization/Authz.cs` (build the principal from `CallerIdentity`),
  `Zgw/ZgwTokenProvider.cs` (`Mint(CallerIdentity)`), `Zgw/OpenZaakZaakSource.cs` (BSN filter on
  the citizen read), `Data/IZaakSource.cs` (+ a caller-scoped read), `Program.cs` (replace
  `DemoOwner` call sites with the resolved BSN; DI-register the provider).
- Tests: identity resolution (stub), token carries the per-request user, citizen read filters by
  BSN (stub handler asserts the query param), admin read still cross-owner.

## Steps

1. Add `CallerIdentity` + `IIdentityProvider` + `StubIdentityProvider` (X-Role + X-Subject BSN,
   default = seeded citizen); DI-register; resolve once in middleware into `HttpContext.Items`.
2. Route `Authz.ResolvePrincipal` and every `DemoOwner` call site through the resolved identity.
3. `ZgwTokenProvider.Mint(caller)` — per-request `user_id`/`user_representation`.
4. Add a caller-scoped cases read to `IZaakSource` (+ both impls); `OpenZaakZaakSource` adds the
   `rol__…__inpBsn` filter; local uses `ApplicationStore.List(owner)`.
5. Tests as above; keep the admin list unchanged.

## Acceptance criteria

- [ ] No `DocumentStore.DemoOwner` reference remains in request handling (grep clean); ownership
      comes from the resolved identity.
- [ ] ZGW JWT carries the acting citizen's `user_id`/`user_representation` (test-verified).
- [ ] A citizen read returns only that BSN's zaken (local + ZGW-stub tests); admin read unchanged.
- [ ] `dotnet test` green; `npm run ci` green with **no api-client drift** (FE contract intact).

## Verification

`cd backend && dotnet test`; manual: `X-Role`/`X-Subject` (or `?role=`) still switches identity
offline; with `Zgw:Enabled=true` (WP-54 harness) a citizen sees only their zaken.

## Out of scope

Real DigiD/OIDC/JWT validation (this is the seam + stub only), FE login redesign, multi-tab
session sync (CLAUDE.md out-of-scope list).

## Risks

- Missing a `DemoOwner` call site → a citizen sees another's data. Mitigate: grep gate in the
  acceptance criteria + a test that two identities don't see each other's cases.
- ZGW rol filter param name is exact and version-sensitive; assert it in the stub-handler test.