feat(portal-bff): msal confidential client provider in AuthModule (#104)

Second step of ADR-0009 wiring. AuthModule now exposes the
`@azure/msal-node` confidential client alongside the parsed Entra
config — the building block the upcoming OIDC routes inject to issue
the auth-code URL, exchange the callback code for tokens, and
acquire downstream tokens on behalf of the user.

What lands:

- `@azure/msal-node` added as a direct dependency (^5.2.1).
- `apps/portal-bff/src/auth/msal-client.token.ts` — `MSAL_CLIENT`
  string token + `ConfidentialClientApplication` type re-export.
  Mirrors the `ENTRA_CONFIG` token shape from PR #102.
- AuthModule grows a factory provider for `MSAL_CLIENT`:
  - Injects `ENTRA_CONFIG` + nestjs-pino `Logger`.
  - Builds a `ConfidentialClientApplication` with `clientId`,
    `authority`, `clientSecret` from the parsed config.
  - Wires `system.loggerOptions.loggerCallback` to forward MSAL's
    internal log lines into the Pino stream (per ADR-0012) — Error
    → logger.error, Warning → logger.warn, Verbose / Trace →
    logger.debug, Info → logger.log. PII logging is disabled by
    default so tokens / user identifiers never leak into our
    structured log records.
  - Sets MSAL's `logLevel` to Info — Pino's own threshold
    re-filters from there.
  - All MSAL log lines carry the `msal` Pino context for easy
    isolation in log queries.
- `AuthModule.exports` extended to include `MSAL_CLIENT`.

Verification:

- `nx run-many -t lint test build --projects=portal-bff` — green.
- 30/30 specs (was 29; +1 covering MSAL client construction).
- New spec imports `nestjs-pino`'s `LoggerModule.forRoot({ pinoHttp:
  { level: 'silent' } })` to provide the same Logger the production
  app supplies via `ObservabilityModule`, without flooding test
  stdout. Two tests assert the provider tree resolves correctly
  (ENTRA_CONFIG + MSAL_CLIENT) and one re-checks the missing-env
  failure mode still propagates through the new factory.

Construction is cheap — MSAL Node defers authority discovery to the
first auth call — so the client is built eagerly at module init.
The factory is injection-only; no MSAL methods get invoked yet.
Routes land in the next PR.

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## Summary

## Motivation

## Implementation notes

## Verification

- [ ] `pnpm ci:check` green locally
- [ ] `pnpm ci:audit` green (or pre-existing drift acknowledged)
- [ ] Tested manually:
- [ ] Architecture diagram updated (if `docs/architecture.md` was affected)
- [ ] ADR amended or added (if a decision changed)

## Related

---------

Co-authored-by: Julien Gautier <julien.gautier@apf.asso.fr>
Reviewed-on: #104

apps/portal-bff/src/auth/auth.module.spec.ts

@@ -1,6 +1,9 @@
+import { ConfidentialClientApplication } from '@azure/msal-node';
 import { Test } from '@nestjs/testing';
+import { LoggerModule } from 'nestjs-pino';
 import { AuthModule } from './auth.module';
 import { ENTRA_CONFIG, type EntraConfig } from './entra-config.token';
+import { MSAL_CLIENT } from './msal-client.token';
 
 const VALID = {
   ENTRA_INSTANCE_URL: 'https://login.microsoftonline.com/',
@@ -11,6 +14,17 @@ const VALID = {
   ENTRA_POST_LOGOUT_REDIRECT_URI: 'http://localhost:4200/',
 };
 
+// AuthModule's MSAL_CLIENT factory injects the Pino-backed `Logger`
+// (which the production app supplies through `ObservabilityModule`).
+// Importing `LoggerModule.forRoot({ pinoHttp: { level: 'silent' } })`
+// here registers the same provider for the testing module without
+// flooding test stdout.
+async function compile() {
+  return Test.createTestingModule({
+    imports: [LoggerModule.forRoot({ pinoHttp: { level: 'silent' } }), AuthModule],
+  }).compile();
+}
+
 describe('AuthModule', () => {
   const originalEnv: Record<string, string | undefined> = {};
 
@@ -33,16 +47,20 @@ describe('AuthModule', () => {
   });
 
   it('provides EntraConfig via the ENTRA_CONFIG token', async () => {
-    const ref = await Test.createTestingModule({ imports: [AuthModule] }).compile();
+    const ref = await compile();
     const config = ref.get<EntraConfig>(ENTRA_CONFIG);
     expect(config.clientId).toBe(VALID.ENTRA_CLIENT_ID);
     expect(config.authority).toBe(`${VALID.ENTRA_INSTANCE_URL}${VALID.ENTRA_TENANT_ID}`);
   });
 
+  it('provides a ConfidentialClientApplication via the MSAL_CLIENT token', async () => {
+    const ref = await compile();
+    const client = ref.get<ConfidentialClientApplication>(MSAL_CLIENT);
+    expect(client).toBeInstanceOf(ConfidentialClientApplication);
+  });
+
   it('fails to compile when an env var is missing', async () => {
     delete process.env['ENTRA_CLIENT_SECRET'];
-    await expect(Test.createTestingModule({ imports: [AuthModule] }).compile()).rejects.toThrow(
-      /ENTRA_CLIENT_SECRET/,
-    );
+    await expect(compile()).rejects.toThrow(/ENTRA_CLIENT_SECRET/);
   });
 });