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.

<!--
PR title format — becomes the squash-merge subject on main, validated by commitlint.

  <type>(<scope>): <short description>

Examples:
  feat(portal-shell): add user-preferences panel skeleton
  fix(portal-bff): correct env var bracket access
  docs(decisions): add ADR-0018 for security baseline
  chore(deps): bump @nx/* to 22.7.2

Imperative mood, lowercase, no trailing period, target ≤ 70 chars.
See docs/development.md §5 for the full convention (types, scopes).
-->

## 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.ts

@@ -1,20 +1,29 @@
+import { ConfidentialClientApplication, LogLevel } from '@azure/msal-node';
 import { Module } from '@nestjs/common';
+import { Logger } from 'nestjs-pino';
 import { assertEntraConfig } from '../config/check-entra-config';
-import { ENTRA_CONFIG } from './entra-config.token';
+import { ENTRA_CONFIG, type EntraConfig } from './entra-config.token';
+import { MSAL_CLIENT } from './msal-client.token';
 
 /**
- * Auth module — owns the Entra ID configuration and (in subsequent
- * PRs) the MSAL Node confidential client, the OIDC routes, the
+ * Auth module — owns the Entra ID configuration, the MSAL Node
+ * confidential client, and (in subsequent PRs) the OIDC routes, the
  * session integration, and the route guards. Per ADR-0009.
  *
- * v1 of this module exposes a single provider: the parsed Entra
- * config, available via the `ENTRA_CONFIG` injection token. The
- * factory delegates to `assertEntraConfig()` — the same validator
- * `main.ts` calls at boot — so the typed config object that
- * consumers receive is guaranteed to be complete and well-formed.
- * The duplicate call is intentional: boot-time fails fast, the
- * factory parses again for the DI result. Both reads are
- * idempotent and trivially cheap.
+ * v1 providers:
+ *
+ *   - `ENTRA_CONFIG` — the parsed, validated Entra app-registration
+ *     config (PR #102).
+ *   - `MSAL_CLIENT` — a `ConfidentialClientApplication` instance
+ *     wired with that config plus a logger callback that forwards
+ *     MSAL's internal log lines into the Pino stream so auth flow
+ *     diagnostics land alongside the rest of the BFF logs (per
+ *     ADR-0012). PII logging is disabled by default — MSAL won't
+ *     include tokens or user identifiers in the messages it emits.
+ *
+ * The module stays non-global: modules state "I depend on auth" by
+ * importing it. Re-exports both tokens so a single
+ * `imports: [AuthModule]` is enough to consume either.
  */
 @Module({
   providers: [
@@ -22,7 +31,47 @@ import { ENTRA_CONFIG } from './entra-config.token';
       provide: ENTRA_CONFIG,
       useFactory: () => assertEntraConfig(),
     },
+    {
+      provide: MSAL_CLIENT,
+      inject: [ENTRA_CONFIG, Logger],
+      useFactory: (config: EntraConfig, logger: Logger) =>
+        new ConfidentialClientApplication({
+          auth: {
+            clientId: config.clientId,
+            authority: config.authority,
+            clientSecret: config.clientSecret,
+          },
+          system: {
+            loggerOptions: {
+              piiLoggingEnabled: false,
+              logLevel: LogLevel.Info,
+              loggerCallback: (level, message) => {
+                // MSAL levels: 0=Error, 1=Warning, 2=Info, 3=Verbose, 4=Trace.
+                // Forward to Pino with the matching level. The whole
+                // payload lives under the `msal` context key so a log
+                // search filtering on `msal` returns every MSAL line
+                // without false positives from app code.
+                const ctx = 'msal';
+                switch (level) {
+                  case LogLevel.Error:
+                    logger.error(message, ctx);
+                    break;
+                  case LogLevel.Warning:
+                    logger.warn(message, ctx);
+                    break;
+                  case LogLevel.Verbose:
+                  case LogLevel.Trace:
+                    logger.debug(message, ctx);
+                    break;
+                  default:
+                    logger.log(message, ctx);
+                }
+              },
+            },
+          },
+        }),
+    },
   ],
-  exports: [ENTRA_CONFIG],
+  exports: [ENTRA_CONFIG, MSAL_CLIENT],
 })
 export class AuthModule {}