# WP-18 — ABAC capability spine (Principal + capabilities, phase P1)

Status: todo
Phase: 5 — productie-volwassenheid

## Why

The single biggest gap between this POC and a production SSP: identity carries no
roles/capabilities (`Session { bsn, naam }` only), the only "role" is an unverified
`?role=` query param stamped as an `X-Role` header, and `BriefStore.editable`
computes its authorization gate **in the frontend** from that header — the exact
anti-pattern ADR-0001 exists to prevent (FE renders decisions, never computes them).
The backend is fully open: no `[Authorize]`, no principal, ownership is a constant
`DemoOwner`. ADR-0002 and PRD-0002 already designed the fix; nothing is built. This
WP implements PRD-0002's **P1 — Capability spine** only (§9), the smallest slice
that closes the anti-pattern and gives every later phase (data-scoping, PII
redaction, step-up/audit) a real foundation to extend.

## Read first

- `docs/architecture/0002-user-groups-and-bounded-contexts.md` (the `Principal`
  union, identity-vs-authorization split)
- `docs/prd/0002-attribute-based-access-control.md` §5a, §6, §7, §9-P1 (this WP
  implements exactly P1 — don't reach into P2/P3)
- `src/app/auth/domain/session.ts` (flat `Session` to replace)
- `src/app/auth/application/session.store.ts`, `src/app/auth/auth.guard.ts` (seams
  that already localise the `Session → Principal` swap, per ADR-0002)
- `src/app/shared/domain/role.ts`, `src/app/shared/infrastructure/role.ts` +
  `role.interceptor.ts` (the dev stub being retired as an authority, kept as a dev
  toggle)
- `src/app/brief/application/brief.store.ts:28,41-46` (`readonly role = currentRole()`
  and the `editable` computed — the FE-computed gate to remove)
- `backend/src/BigRegister.Api/Contracts/Dtos.cs:25-27` (`HerregistratieDecisionsDto`
  — the decision-flag pattern this WP extends to a `BriefDecisionsDto`)
- `backend/src/BigRegister.Api/Program.cs:318-335` (`IsAdmin`, the `X-Role` reader
  around brief endpoints — becomes `Authz.Can`)
- `backend/src/BigRegister.Api/Data/BriefStore.cs` (`Review`, the
  `actingId == e.DrafterId → Forbidden` SoD check — keep this check, move it behind
  the verified principal)

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

- **P1 scope only.** No data-scoping, no PII redaction/BSN reveal, no step-up or
  audit log — those are PRD-0002 §9 P2/P3, separate future WPs. This WP: `Principal`,
  `AccessStore`/`can()`, `capabilityGuard`, `GET /me`, capability flags on the brief
  screen DTO, and server-side enforcement via one shared `Authz.Can` helper.
- **The AD/OIDC identity provider stays simulated** (PRD-0002 §3 non-goal). The
  `Principal` is still built server-side from the existing dev stand-ins
  (`X-Role`/`X-Admin` headers), but it becomes the backend's own construct — the FE
  never re-derives capabilities from the header, it only reads what the backend sends.
- **Capability naming**: stable, namespaced strings per PRD-0002 §5a — start with
  exactly `brief:approve`, `brief:reject`, `brief:send` (the brief flow is the only
  role-gated flow that exists today). Do not invent capabilities for flows that don't
  exist yet (e.g. `aanvraag:beoordelen` — that's the backoffice, ADR-0002, out of scope).
- **Emit and enforce are the same code path.** `Authz.Can(principal, action, resource)`
  is called both to compute the DTO flag and to gate the endpoint — never two separate
  checks that can drift (PRD-0002 §7, the classic BOLA bug it calls out).
- **Dev role toggle survives**, but moves behind the `Principal` seam: `?role=` still
  picks an identity for demo purposes, but it flows into building the `Principal`
  server-side (still asserted by the client — this is _not_ real auth, just moving
  the authority from FE-computed to BE-computed within the POC's honesty envelope).
  Keep it explicitly commented `// dev stub — NOT a security boundary` per PRD-0002 §3.

## Files

- `src/app/auth/domain/session.ts` — replace `Session` with the `Principal`
  discriminated union from ADR-0002 (`{ kind: 'zorgverlener'; bsn; naam }` — no
  `medewerker` variant yet, that's ADR-0002/backoffice scope; keep the union shape so
  it's additive later). Update `isAuthenticated`.
- `src/app/auth/application/session.store.ts` — carries the `Principal`; unchanged
  persistence rules (never persist the BSN, per existing comment).
- New `src/app/shared/domain/capability.ts` — branded/union `Capability` type
  (`'brief:approve' | 'brief:reject' | 'brief:send'`), framework-free.
- New `src/app/shared/application/access.store.ts` — `providedIn: 'root'`, holds
  resolved capabilities as `RemoteData` from `GET /me`; `can(capability): boolean`,
  deny-by-default on absence.
- New `src/app/shared/infrastructure/me.adapter.ts` (+ spec) — calls `GET /me`,
  `parseMe(): Result` boundary.
- New `capabilityGuard` in `src/app/auth/auth.guard.ts` (or co-located
  `capability.guard.ts`) — factory `CanActivateFn` extending `authGuard`'s shape.
- `src/app/brief/application/brief.store.ts` — delete `readonly role = currentRole()`
  and the FE-computed `editable`; read `canApprove`/`canReject`/`canSend` off the
  loaded `BriefViewDto`'s new `BriefDecisionsDto` instead.
- `src/app/shared/infrastructure/role.interceptor.ts` — keep (still asserts the dev
  identity), retitle its comment to "feeds Principal construction, not an authority
  the FE reads back."
- Backend: `backend/src/BigRegister.Api/Contracts/Dtos.cs` — add
  `BriefDecisionsDto(bool CanApprove, bool CanReject, bool CanSend)`; add it to
  `BriefViewDto`.
- New `backend/src/BigRegister.Api/Domain/Authorization/Principal.cs` +
  `Authz.cs` — `Principal` (mirrors the FE union), `Authz.Can(principal, action)`
  covering the three brief capabilities + the existing SoD rule.
- `backend/src/BigRegister.Api/Program.cs` — add `GET /api/v1/me` returning the
  resolved `Principal`'s capabilities; replace the ad-hoc `X-Role` reads around
  brief endpoints with `Authz.Can`; compute `BriefDecisionsDto` via the same helper.
- New backend test `backend/tests/BigRegister.Tests/AuthzTests.cs` — `Authz.Can`
  unit tests (approve/reject/send × drafter/approver × SoD).

## Steps

1. Backend: `Principal`, `Authz.Can`, `GET /me`, `BriefDecisionsDto` wired into the
   existing brief endpoints (replace `IsDrafter`/`X-Role` reads one at a time,
   keeping `BriefEndpointTests.cs` green after each).
2. FE: `Capability` type, `access.store.ts`, `me.adapter.ts`, `capabilityGuard`.
3. FE: `Session → Principal` in `auth/domain`; thread through `SessionStore`,
   `auth.guard.ts` (both keep working — `isAuthenticated` still means "has a
   Principal").
4. FE: `brief.store.ts` reads `canApprove`/`canReject`/`canSend` from the DTO;
   delete `currentRole()` import and the FE-computed `editable`. Update the brief
   UI components consuming `.editable`/`.role` to consume the new flags.
5. Update PRD-0002's own status: this WP completes phase P1 — note it in the PRD or
   leave for a follow-up doc pass (don't rewrite the PRD's phasing table mid-WP).

## Acceptance criteria

- [ ] `brief.store.ts` contains no `currentRole()` call and no FE-computed
      permission boolean; `canApprove`/`canReject`/`canSend` come from the DTO.
- [ ] Forging `?role=approver` in the browser with a stale/absent server capability
      still gets a 403 from the backend (verified by a test hitting the endpoint
      directly, bypassing the FE).
- [ ] `Authz.Can` is the only place brief authorization logic lives; the emit path
      (DTO flags) and the enforce path (endpoint gating) both call it.
- [ ] `GET /me` returns capabilities; `AccessStore.can()` defaults to `false` for an
      unknown capability.
- [ ] The existing SoD rule (approver ≠ drafter) still holds, now expressed as an
      `Authz.Can` precondition rather than inline in `BriefStore.Review`.
- [ ] `capabilityGuard` compiles and is demonstrated on at least one route (or
      documented as available-but-unwired if no route needs it yet — brief has no
      route today, it's a page section).

## Verification

GREEN (`docs/backlog/README.md`) + `cd backend && dotnet test`. Manual smoke:
`npm start` with `?role=drafter` — draft-only actions enabled; `?role=approver` —
approve/reject enabled, editing disabled. Confirm via browser devtools that removing
the `X-Role` header (or backend patched to ignore it) makes every capability `false`
— i.e. deny-by-default actually denies.

## Out of scope

PRD-0002 P2 (data-scoping, PII/BSN redaction) and P3 (step-up, break-glass, audit
log) — separate future WPs. The Behandeling/backoffice app and `medewerker`
`Principal` variant (ADR-0002 — no second actor exists yet, still YAGNI). Real
AD/OIDC integration (identity provider stays simulated).

## Risks

Threading `Principal` through `SessionStore`/`auth.guard.ts` touches the one
authenticated-session seam every route depends on — keep the observable shape
(`isAuthenticated(): boolean`) identical so no route wiring needs to change, only
what's inside `Session`/`Principal`. Backend `Authz.Can` replacing inline `X-Role`
reads must preserve the existing 403 `Outcome.Forbidden` mapping
(`Program.cs:330-335`) exactly, or `BriefEndpointTests.cs` breaks.