## Summary
First step in the `portal-admin` audit-log-viewer workstream (per [ADR-0020](docs/decisions/0020-portal-admin-app.md)). The BFF's `AdminRoleGuard` (next PR) needs to read `session.user.roles` to enforce admin-only access to `/api/admin/*`. Today the session carries `{ oid, tid, username, displayName, amr }` — the `roles` claim is dropped on the floor when the ID token comes back from Entra.
This PR closes that gap:
- Adds `roles: readonly string[]` to [AuthenticatedUser](apps/portal-bff/src/auth/auth.service.ts) and threads it through `toAuthenticatedUser()`.
- The field flows onto `req.session.user` automatically via the existing module-augmentation chain in [session.types.ts](apps/portal-bff/src/session/session.types.ts) — no extra wiring.
## Defensive parsing
Mirrors the existing `amr` extraction pattern:
| Input claim shape | Result |
| --- | --- |
| `["admin", "editor"]` | `["admin", "editor"]` |
| Claim absent | `[]` |
| Non-array (e.g. `"admin"`) | `[]` |
| Mixed types (e.g. `["admin", 42, null, "editor"]`) | `["admin", "editor"]` |
Empty array means **"user has no app role assigned"**, not **"claim was unparseable"** — both collapse to the same value because both are equally non-authoritative for the admin guard.
## Why this is its own PR
The `AdminRoleGuard` + `@RequireAdmin()` decorator + first `/api/admin/me` self-test endpoint will follow in the next PR. Splitting the claim extraction out makes both diffs trivial to read and lets the second PR focus on guard semantics + audit emission without the mechanical fixture updates that came with adding a new `AuthenticatedUser` field.
## Surface impact — none yet
- `PublicUser` (the SPA-facing shape returned by `GET /api/auth/me`) is **deliberately unchanged**. Exposing `roles` to the SPA happens in the next PR alongside the conditional admin-link rendering — without a consumer in this PR it would be dead code.
- Audit pipeline unchanged. `SignInActor` carries `{ oid, amr }` only; the audit log doesn't need `roles` and won't get it.
- No new env vars, no new dependencies.
## Test plan
- [x] `pnpm nx test portal-bff` — **203 specs pass** (was 199; +4 new specs covering the four parsing cases above).
- [x] `pnpm exec nx affected -t format:check lint test build --base=origin/main` — clean (the pre-existing `_res` / `_next` warnings in `rate-limit.middleware.ts` are unrelated).
- [x] Existing fixtures in [auth.controller.spec.ts](apps/portal-bff/src/auth/auth.controller.spec.ts), [auth.service.spec.ts](apps/portal-bff/src/auth/auth.service.spec.ts), [absolute-timeout.middleware.spec.ts](apps/portal-bff/src/session/absolute-timeout.middleware.spec.ts) updated with `roles: []`.
- [ ] e2e — would require the `admin` app role to be declared on the Entra registration and assigned to a test user. Out of scope for this PR; will be validated when the `AdminRoleGuard` lands and there is a 403 to observe.
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Co-authored-by: Julien Gautier <julien.gautier@apf.asso.fr>
Reviewed-on: #126
julien
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