julien
d665c66c4e
## Summary
First half of the **DownstreamApiClient + OBO** chantier per [ADR-0014](docs/decisions/0014-downstream-api-access-obo-pattern.md). Ships the OBO auth strategy and its encrypted-at-rest token cache as testable primitives — explicitly **not** the full `DownstreamApiClientFactory` + cockatiel + audience-pre-check framework.
The scope is dictated by ADR-0014 §"Consequences":
> *"Bad, because the framework is forward-looking — there is no concrete v1 caller. Risk of drift between framework and real needs. **Mitigated by writing the framework code only in the same iteration as the first concrete integration; until then, this ADR plus mock-driven unit tests on the strategies (OBO, signed-assertion) keep the design honest.**"*
The framework gets assembled when the first real downstream integration arrives, with that integration as the validation surface. The next PR in this chantier ships the symmetric signed-assertion strategy + the JWKS endpoint.
## What lands
### [`assertOboCacheEncryptionKey`](apps/portal-bff/src/config/check-obo-cache-encryption-key.ts)
Boot validator mirroring `assertSessionEncryptionKey`. AES-256-GCM, 32-byte requirement, placeholder rejection, fail-fast posture. Plus one extra defense in depth:
> *Refuses a value identical to `SESSION_ENCRYPTION_KEY`* — ADR-0014 §"Token cache (for OBO)" mandates dedicated keys; catching the copy-paste regression at boot prevents a silent trust-boundary downgrade.
Wired in [`main.ts`](apps/portal-bff/src/main.ts) alongside the other `assertX()` validators.
### [`DownstreamTokenCache`](apps/portal-bff/src/downstream/downstream-token-cache.service.ts)
Redis-backed cache, key shape `obo:{actorIdHash}:{resource}`. Encrypts each entry via the shared AES-256-GCM helpers from `session-crypto` but under a **dedicated key** (`OBO_CACHE_KEY`).
| Path | Behaviour |
| --- | --- |
| Cache miss | Returns `null`. |
| Tampered ciphertext | Returns `null` + Pino warn `downstream.obo_cache.decrypt_failed`. |
| Wrong-key ciphertext | Returns `null` (GCM auth-tag mismatch). |
| Decrypted but malformed shape | Returns `null` + Pino warn. |
| Redis read failure | Returns `null` + Pino warn `downstream.obo_cache.read_failed`. |
| Write of a token already inside the 60 s buffer | Skipped (TTL would be useless). |
| Redis write failure | Logged, non-fatal. |
Reads never throw — every failure collapses to a miss, the strategy re-acquires from Entra.
### [`OboStrategy`](apps/portal-bff/src/downstream/strategies/obo.strategy.ts)
Wraps MSAL Node's `acquireTokenOnBehalfOf` with the cache.
```
acquire(input):
cached = cache.get(...)
if cached && cached.expiresAt - now > 60s → return cached
result = msal.acquireTokenOnBehalfOf({ oboAssertion, scopes })
if !result || !result.accessToken || !result.expiresOn → throw OboAcquireError(msal-no-result)
cache.set(...)
return result
```
`OboAcquireError` carries a typed `reason` discriminator (`msal-refused` / `msal-no-result`) the future framework will translate to a **502 + `auth.token.validation.failed`** audit event per ADR-0014 — "the BFF does NOT silently fall back to the user's original token".
### One scope nuance from ADR-0014
ADR-0014 §"OBO strategy" says *"uses MSAL Node's `acquireTokenOnBehalfOf` with the user's current Entra access token (read from session via CLS)"*. v1 sessions don't persist the user's access token (ADR-0009 omits `offline_access` deliberately). For now the strategy takes the user access token as an **input parameter** — when the first concrete integration ships, the framework will fetch it from CLS / MSAL's token cache and forward here. That keeps the strategy a testable primitive without coupling to a session shape that doesn't exist yet.
### [`DownstreamModule`](apps/portal-bff/src/downstream/downstream.module.ts)
Provides `OBO_CACHE_KEY` (via the validator at factory time), `DownstreamTokenCache`, `OboStrategy`. Imports `AuthModule` for the shared `MSAL_CLIENT` and `RedisModule` for the shared `ioredis` client. Wired into `AppModule` though no runtime consumer yet — the registration makes the strategy injectable for the future integration without that integration having to also touch the module graph.
## Required env update (mandatory at boot)
```env
OBO_CACHE_ENCRYPTION_KEY=replace_with_32_random_bytes_base64url
```
Generate with `node -e "console.log(require('crypto').randomBytes(32).toString('base64url'))"`. Must differ from `SESSION_ENCRYPTION_KEY` — the boot validator refuses identical values.
## Out of scope (deferred until the first concrete integration)
Per ADR-0014's "until then" clause:
- `DownstreamApiClientFactory` + per-service typed config.
- `cockatiel` resilience composition (timeout, retry, circuit breaker, bulkhead).
- Audience pre-check at the call site (`audienceConstraint` → `authz.deny` audit event).
- Error-translation tables per service.
- OTel custom spans `downstream.<service>.<verb>.<path>`.
- The `auth.token.validation.failed` audit event itself (the discriminator is on `OboAcquireError`, the audit-emission glue lives in the future framework).
- The framework wiring that reads the user access token from CLS instead of accepting it as a parameter.
These land alongside the first concrete integration so the framework shape is validated against a real consumer, not speculative needs.
## Test plan
- [x] `pnpm nx test portal-bff` — **334 specs pass** (was 308; +26: env validator 8, token cache 9, OBO strategy 9).
- [x] `pnpm exec nx affected -t format:check lint test build --base=origin/main` — clean.
- [x] Env validator refuses placeholder, wrong length, non-base64url, AND identical-to-`SESSION_ENCRYPTION_KEY`. Boot-order tolerant: accepts the value when `SESSION_ENCRYPTION_KEY` is unset.
- [x] Token cache round-trip verified: written ciphertext starts with `v1.`, never contains the plaintext sentinel.
- [x] Tamper rejection verified: flipping the last char of the GCM-encrypted blob fails decryption and collapses to a miss.
- [x] Wrong-key rejection verified: writing with one key, reading with another, returns `null`.
- [x] TTL math verified: PX TTL = `expiresAt − now − 60 000`. Write skipped when token already inside the buffer.
- [x] OBO strategy: cache-hit short-circuit, stale-cache re-acquire, cold-cache → MSAL → cache.set, MSAL refusal → typed error, MSAL null-result → typed error, empty access token → typed error, null expiresOn → typed error.
## Notes for the reviewer
- The strategy file uses `override readonly cause` on `OboAcquireError` because TS `strict.exactOptionalPropertyTypes + noImplicitOverride` flags shadowing the built-in `Error.cause`. The shadowing is intentional — we want the typed cause property visible in error consumers — so the `override` keyword is the canonical way.
- `DownstreamTokenCache.get`'s "never throws" posture is deliberate. A cache failure must not poison a downstream call: the strategy re-acquires from Entra. The trade-off is that a key-rotation gone wrong shows up as silent re-acquisitions (no errors, just extra MSAL load); the structured Pino warns are the ops signal.
- The `DownstreamModule` is wired into `AppModule` even though nothing consumes the strategy at runtime. Without the wiring, the first integration PR would have to also touch the module graph; with it, the integration is just "inject `OboStrategy` and call `.acquire()`".
---------
Co-authored-by: Julien Gautier <julien.gautier@apf.asso.fr>
Reviewed-on: #137
Documentation index
This is the entry point to all project documentation. It is maintained automatically: any addition, rename, or removal of a .md file under docs/ must be reflected here in the same change.
Conventions
- Documentation is written in English.
- One topic per file. Group related files into a folder when there are three or more.
- Cross-reference with relative links so they keep working in GitHub, IDEs, and exported sites.
- For architectural decisions, do not add them here — they belong in decisions/ as MADR 4.0.0 ADRs.
Sections
Daily development
- development.md — repo layout, prerequisites, initial setup, daily commands, observability dev-loop (Jaeger UI, log ↔ trace correlation), dependency updates (Renovate), conventional commit cycle. Day-to-day reference for working on the project.
Architecture
- architecture.md — cross-cutting Mermaid diagrams: C4 system context, C4 containers, Nx module boundaries, CI/CD pipeline. Single-decision diagrams (auth sequence, ERD, etc.) live inline in their ADR.
Onboarding & environment
Setup guides for new contributors:
- setup/01-wsl-terminal-setup.md — modern WSL terminal (Zsh + Powerlevel10k + CLI tools)
- setup/02-dev-web-stack.md — Node via nvm, pnpm via corepack, Docker
- setup/03-angular-nx-monorepo.md — Angular + Nx monorepo bootstrap
Operations & runbooks
Empty — to be populated when we deploy.
Security, performance, accessibility
Empty — placeholders to be filled with rationale docs alongside their corresponding ADRs.