apps/portal-shell/src/app/app.config.ts

@@ -5,6 +5,8 @@ import {
 } from '@angular/core';
 import { provideHttpClient, withFetch } from '@angular/common/http';
 import { provideRouter } from '@angular/router';
+import { AUTH_BFF_BASE_URL } from 'feature-auth';
+import { environment } from '../environments/environment';
 import { appRoutes } from './app.routes';
 
 export const appConfig: ApplicationConfig = {
@@ -18,5 +20,9 @@ export const appConfig: ApplicationConfig = {
     // the W3C `traceparent` header propagated to the BFF
     // automatically. The legacy XHR backend would short-circuit that.
     provideHttpClient(withFetch()),
+    // `feature-auth` is environment-agnostic and reads the BFF base
+    // URL from this token — provided once per app from `environment.ts`
+    // (per ADR-0018).
+    { provide: AUTH_BFF_BASE_URL, useValue: environment.bffApiBaseUrl },
   ],
 };

apps/portal-shell/src/app/app.spec.ts

@@ -1,12 +1,22 @@
+import { provideHttpClient } from '@angular/common/http';
+import { HttpTestingController, provideHttpClientTesting } from '@angular/common/http/testing';
 import { TestBed } from '@angular/core/testing';
 import { provideRouter } from '@angular/router';
+import { AUTH_BFF_BASE_URL } from 'feature-auth';
 import { App } from './app';
 
+const BFF_BASE = 'http://bff.test/api';
+
 describe('App', () => {
   beforeEach(async () => {
     await TestBed.configureTestingModule({
       imports: [App],
-      providers: [provideRouter([])],
+      providers: [
+        provideRouter([]),
+        provideHttpClient(),
+        provideHttpClientTesting(),
+        { provide: AUTH_BFF_BASE_URL, useValue: BFF_BASE },
+      ],
     }).compileComponents();
   });
 
@@ -19,5 +29,10 @@ describe('App', () => {
     expect(root.querySelector('app-sidebar')).not.toBeNull();
     expect(root.querySelector('main#main-content')).not.toBeNull();
     expect(root.querySelector('app-footer')).not.toBeNull();
+    // Drain the bootstrap /me request fired by the Header's AuthService.
+    const httpCtrl = TestBed.inject(HttpTestingController);
+    httpCtrl
+      .expectOne(`${BFF_BASE}/auth/me`)
+      .flush({}, { status: 401, statusText: 'Unauthorized' });
   });
 });

apps/portal-shell/src/app/components/header/header.html

@@ -70,13 +70,58 @@
       >
         <lib-icon name="settings" />
       </button>
+
+      @switch (authState().kind) { @case ('loading') {
       <span
-        i18n-aria-label="@@header.action.userMenu"
+        aria-hidden="true"
-        aria-label="User menu (coming soon)"
+        class="ml-1 inline-flex h-9 w-9 items-center justify-center rounded-full bg-gray-200 text-sm font-semibold text-gray-500 dark:bg-gray-700 dark:text-gray-300"
+      >
+        …
+      </span>
+      <span class="sr-only" i18n="@@header.userMenu.loading">Checking sign-in status…</span>
+      } @case ('anonymous') {
+      <button
+        type="button"
+        (click)="signIn()"
+        class="ml-1 inline-flex h-11 items-center gap-2 rounded-full bg-brand-primary-500 px-4 text-sm font-semibold text-white transition-colors hover:bg-brand-primary-600 focus-visible:outline-2 focus-visible:outline-offset-2 focus-visible:outline-brand-primary-500"
+        data-testid="sign-in-button"
+        i18n="@@header.signIn"
+      >
+        Sign in
+      </button>
+      } @case ('authenticated') { @if (authState(); as state) { @if (state.kind === 'authenticated')
+      {
+      <span
+        aria-hidden="true"
+        data-testid="user-avatar"
         class="ml-1 inline-flex h-9 w-9 items-center justify-center rounded-full bg-brand-primary-500 text-sm font-semibold text-white"
       >
-        ?
+        {{ initials() }}
       </span>
+      <span
+        class="hidden text-sm font-medium text-gray-700 sm:inline dark:text-gray-200"
+        data-testid="user-displayname"
+        >{{ state.user.displayName }}</span
+      >
+      <button
+        type="button"
+        (click)="signOut()"
+        class="inline-flex h-11 items-center gap-2 rounded-full px-3 text-sm font-medium text-gray-600 transition-colors hover:bg-gray-100 hover:text-brand-primary-500 focus-visible:outline-2 focus-visible:outline-offset-2 focus-visible:outline-brand-primary-500 dark:text-gray-300 dark:hover:bg-gray-800 dark:hover:text-brand-primary-300"
+        data-testid="sign-out-button"
+        i18n="@@header.signOut"
+      >
+        Sign out
+      </button>
+      } } } @case ('error') {
+      <span
+        class="ml-1 inline-flex h-9 items-center rounded-full bg-amber-100 px-3 text-sm font-medium text-amber-800 dark:bg-amber-900 dark:text-amber-200"
+        data-testid="auth-error"
+        role="status"
+        i18n="@@header.authError"
+      >
+        Can't reach the server
+      </span>
+      } }
     </nav>
   </div>
 </header>

apps/portal-shell/src/app/components/header/header.spec.ts

@@ -1,35 +1,73 @@
+import { provideHttpClient } from '@angular/common/http';
+import { HttpTestingController, provideHttpClientTesting } from '@angular/common/http/testing';
 import { TestBed } from '@angular/core/testing';
 import { provideRouter } from '@angular/router';
+import { AUTH_BFF_BASE_URL, type CurrentUser } from 'feature-auth';
 import { Header } from './header';
-import { LayoutStateService } from 'shared-state';
+
+const BFF_BASE = 'http://bff.test/api';
+const ME_URL = `${BFF_BASE}/auth/me`;
+
+const USER: CurrentUser = {
+  oid: 'user-oid',
+  tid: 'tenant-id',
+  username: 'jane.doe@apf.example',
+  displayName: 'Jane Doe',
+};
+
+async function setup(opts?: { onBootstrap?: 'authenticated' | 'anonymous' | 'error' | 'leave' }) {
+  TestBed.configureTestingModule({
+    imports: [Header],
+    providers: [
+      provideRouter([]),
+      provideHttpClient(),
+      provideHttpClientTesting(),
+      { provide: AUTH_BFF_BASE_URL, useValue: BFF_BASE },
+    ],
+  });
+  const fixture = TestBed.createComponent(Header);
+  const httpCtrl = TestBed.inject(HttpTestingController);
+  // The bootstrap /me fires synchronously in AuthService's
+  // constructor — match and resolve it according to the test's
+  // intent. `leave` keeps the loading state visible.
+  const intent = opts?.onBootstrap ?? 'authenticated';
+  if (intent !== 'leave') {
+    const req = httpCtrl.expectOne(ME_URL);
+    if (intent === 'authenticated') {
+      req.flush(USER);
+    } else if (intent === 'anonymous') {
+      req.flush({ error: 'unauthenticated' }, { status: 401, statusText: 'Unauthorized' });
+    } else {
+      req.flush('boom', { status: 500, statusText: 'Internal Server Error' });
+    }
+    await Promise.resolve();
+  }
+  fixture.detectChanges();
+  await fixture.whenStable();
+  return { fixture, httpCtrl };
+}
 
 describe('Header', () => {
-  beforeEach(async () => {
+  beforeEach(() => {
     localStorage.clear();
-    await TestBed.configureTestingModule({
+    TestBed.resetTestingModule();
-      imports: [Header],
-      providers: [provideRouter([])],
-    }).compileComponents();
   });
 
   it('renders the brand link to /', async () => {
-    const fixture = TestBed.createComponent(Header);
+    const { fixture } = await setup({ onBootstrap: 'anonymous' });
-    await fixture.whenStable();
     const link = fixture.nativeElement.querySelector('a[href="/"]') as HTMLAnchorElement | null;
     expect(link).not.toBeNull();
     expect(link?.textContent?.trim()).toContain('APF Portal');
   });
 
   it('exposes a primary navigation landmark', async () => {
-    const fixture = TestBed.createComponent(Header);
+    const { fixture } = await setup({ onBootstrap: 'anonymous' });
-    await fixture.whenStable();
     const nav = fixture.nativeElement.querySelector('nav[aria-label="Primary"]');
     expect(nav).not.toBeNull();
   });
 
   it('exposes a search landmark with a labelled input', async () => {
-    const fixture = TestBed.createComponent(Header);
+    const { fixture } = await setup({ onBootstrap: 'anonymous' });
-    await fixture.whenStable();
     const root = fixture.nativeElement as HTMLElement;
     expect(root.querySelector('form[role="search"]')).not.toBeNull();
     const input = root.querySelector('input#global-search') as HTMLInputElement | null;
@@ -40,8 +78,7 @@ describe('Header', () => {
   });
 
   it('renders the notifications / help / settings action buttons', async () => {
-    const fixture = TestBed.createComponent(Header);
+    const { fixture } = await setup({ onBootstrap: 'anonymous' });
-    await fixture.whenStable();
     const root = fixture.nativeElement as HTMLElement;
     expect(root.querySelector('button[aria-label="Notifications"]')).not.toBeNull();
     expect(root.querySelector('button[aria-label="Help"]')).not.toBeNull();
@@ -49,15 +86,12 @@ describe('Header', () => {
   });
 
   it('embeds the theme switcher', async () => {
-    const fixture = TestBed.createComponent(Header);
+    const { fixture } = await setup({ onBootstrap: 'anonymous' });
-    await fixture.whenStable();
     expect(fixture.nativeElement.querySelector('app-theme-switcher')).not.toBeNull();
   });
 
   it('renders the logo zone, expanded with wordmark by default', async () => {
-    const fixture = TestBed.createComponent(Header);
+    const { fixture } = await setup({ onBootstrap: 'anonymous' });
-    fixture.detectChanges();
-    await fixture.whenStable();
     const root = fixture.nativeElement as HTMLElement;
     const zone = root.querySelector('.header__logo-zone');
     expect(zone).not.toBeNull();
@@ -66,16 +100,58 @@ describe('Header', () => {
   });
 
   it('collapses the logo zone and hides the wordmark when the sidebar is collapsed', async () => {
-    const layout = TestBed.inject(LayoutStateService);
+    localStorage.setItem('portal-shell:sidebar-collapsed', '1');
-    layout.setSidebarCollapsed(true);
+    const { fixture } = await setup({ onBootstrap: 'anonymous' });
-
-    const fixture = TestBed.createComponent(Header);
-    fixture.detectChanges();
-    await fixture.whenStable();
     const root = fixture.nativeElement as HTMLElement;
     const zone = root.querySelector('.header__logo-zone');
     expect(zone?.classList.contains('header__logo-zone--collapsed')).toBe(true);
-    const wordmark = root.querySelector('a[href="/"] span');
+    // The collapsed brand link contains the logo image only — no
-    expect(wordmark).toBeNull();
+    // wordmark span. We assert by inspecting the link's direct
+    // children.
+    const wordmarkSpan = root.querySelector('a[href="/"] > span');
+    expect(wordmarkSpan).toBeNull();
+  });
+
+  describe('user widget', () => {
+    it('renders a Sign in button when the BFF says anonymous', async () => {
+      const { fixture } = await setup({ onBootstrap: 'anonymous' });
+      const root = fixture.nativeElement as HTMLElement;
+      const btn = root.querySelector('[data-testid="sign-in-button"]') as HTMLButtonElement | null;
+      expect(btn).not.toBeNull();
+      expect(btn?.textContent?.trim()).toBe('Sign in');
+      expect(root.querySelector('[data-testid="user-avatar"]')).toBeNull();
+    });
+
+    it('renders the user avatar + display name + Sign out button when authenticated', async () => {
+      const { fixture } = await setup({ onBootstrap: 'authenticated' });
+      const root = fixture.nativeElement as HTMLElement;
+      const avatar = root.querySelector('[data-testid="user-avatar"]');
+      expect(avatar?.textContent?.trim()).toBe('JD');
+      expect(root.querySelector('[data-testid="user-displayname"]')?.textContent?.trim()).toBe(
+        USER.displayName,
+      );
+      const signOut = root.querySelector(
+        '[data-testid="sign-out-button"]',
+      ) as HTMLButtonElement | null;
+      expect(signOut).not.toBeNull();
+      expect(root.querySelector('[data-testid="sign-in-button"]')).toBeNull();
+    });
+
+    it('shows the error chip when /me fails with a non-401', async () => {
+      const { fixture } = await setup({ onBootstrap: 'error' });
+      const root = fixture.nativeElement as HTMLElement;
+      const chip = root.querySelector('[data-testid="auth-error"]');
+      expect(chip).not.toBeNull();
+      expect(chip?.getAttribute('role')).toBe('status');
+    });
+
+    it('shows the loading placeholder before /me resolves', async () => {
+      const { fixture, httpCtrl } = await setup({ onBootstrap: 'leave' });
+      const root = fixture.nativeElement as HTMLElement;
+      expect(root.querySelector('[data-testid="sign-in-button"]')).toBeNull();
+      expect(root.querySelector('[data-testid="user-avatar"]')).toBeNull();
+      // Drain the still-pending request so the controller stays clean.
+      httpCtrl.expectOne(ME_URL).flush({}, { status: 401, statusText: 'Unauthorized' });
+    });
   });
 });

apps/portal-shell/src/app/components/header/header.ts

@@ -1,8 +1,9 @@
-import { ChangeDetectionStrategy, Component, inject } from '@angular/core';
+import { ChangeDetectionStrategy, Component, computed, inject } from '@angular/core';
 import { RouterLink } from '@angular/router';
+import { AuthService, type CurrentUser } from 'feature-auth';
 import { Icon } from 'shared-ui';
-import { ThemeSwitcher } from '../theme-switcher/theme-switcher';
 import { LayoutStateService } from 'shared-state';
+import { ThemeSwitcher } from '../theme-switcher/theme-switcher';
 
 /**
  * Top-of-page banner.
@@ -15,9 +16,11 @@ import { LayoutStateService } from 'shared-state';
  *     `LayoutStateService`.
  *   - Global search input (placeholder; wired to a real search service
  *     once we have content to query).
- *   - Action cluster: notifications, help, settings, and an avatar
+ *   - Action cluster: notifications, help, settings, and a user
- *     placeholder. Real menus are added once the auth flow lands
+ *     widget. The widget renders one of three states — loading,
- *     (ADR-0009).
+ *     anonymous (a "Sign in" button), authenticated (avatar with
+ *     initials + display name + "Sign out" button) — driven by
+ *     `AuthService` (ADR-0009).
  *
  * Lives at app level (not in libs/shared/ui/) on purpose: one consumer
  * for now. Promotion when a second app needs it.
@@ -31,6 +34,35 @@ import { LayoutStateService } from 'shared-state';
 })
 export class Header {
   private readonly layout = inject(LayoutStateService);
+  private readonly auth = inject(AuthService);
 
   protected readonly collapsed = this.layout.sidebarCollapsed;
+
+  protected readonly authState = this.auth.state;
+
+  protected readonly initials = computed(() => {
+    const user = this.auth.currentUser();
+    return user ? initialsFor(user) : '';
+  });
+
+  protected signIn(): void {
+    this.auth.login();
+  }
+
+  protected signOut(): void {
+    this.auth.logout();
+  }
+}
+
+function initialsFor(user: CurrentUser): string {
+  const name = (user.displayName || user.username).trim();
+  if (!name) {
+    return '?';
+  }
+  const parts = name.split(/\s+/).filter(Boolean).slice(0, 2);
+  const letters = parts.map((p) => p.charAt(0).toUpperCase()).join('');
+  // Fallback to first two chars of the trimmed string when the
+  // split produced an empty array (single-word names with no
+  // whitespace already covered by parts[0]).
+  return letters || name.slice(0, 2).toUpperCase();
 }

apps/portal-shell/src/locale/messages.fr.xlf

@@ -48,9 +48,21 @@
         <source>Settings</source>
         <target>Paramètres</target>
       </trans-unit>
-      <trans-unit id="header.action.userMenu" datatype="html">
+      <trans-unit id="header.authError" datatype="html">
-        <source>User menu (coming soon)</source>
+        <source>Can't reach the server</source>
-        <target>Menu utilisateur (bientôt disponible)</target>
+        <target>Serveur injoignable</target>
+      </trans-unit>
+      <trans-unit id="header.signIn" datatype="html">
+        <source>Sign in</source>
+        <target>Se connecter</target>
+      </trans-unit>
+      <trans-unit id="header.signOut" datatype="html">
+        <source>Sign out</source>
+        <target>Se déconnecter</target>
+      </trans-unit>
+      <trans-unit id="header.userMenu.loading" datatype="html">
+        <source>Checking sign-in status…</source>
+        <target>Vérification de la session…</target>
       </trans-unit>
       <trans-unit id="header.search.label" datatype="html">
         <source>Search the portal</source>

apps/portal-shell/tsconfig.app.json

@@ -7,11 +7,14 @@
   "include": ["src/**/*.ts"],
   "exclude": ["src/**/*.spec.ts", "src/**/*.test.ts"],
   "references": [
+    {
+      "path": "../../libs/shared/state"
+    },
     {
       "path": "../../libs/shared/ui"
     },
     {
-      "path": "../../libs/shared/state"
+      "path": "../../libs/feature/auth"
     }
   ]
 }

libs/feature/auth/src/index.ts

@@ -1 +1,3 @@
-export * from './lib/feature-auth/feature-auth';
+export { AUTH_BFF_BASE_URL, AUTH_NAVIGATOR } from './lib/auth.config';
+export { AuthService } from './lib/auth.service';
+export type { AuthState, CurrentUser } from './lib/auth.types';

libs/feature/auth/src/lib/auth.config.ts

@@ -0,0 +1,28 @@
+import { InjectionToken } from '@angular/core';
+
+/**
+ * BFF API base URL the AuthService prepends to every backend call
+ * (`${base}/auth/me`, `${base}/auth/login`, …). Provided by the host
+ * application from its per-environment config (`environment.ts`,
+ * per ADR-0018) so the lib stays decoupled from the app's
+ * environment file shape.
+ *
+ * Wiring lives in the host's `ApplicationConfig`:
+ *
+ *   { provide: AUTH_BFF_BASE_URL, useValue: environment.bffApiBaseUrl }
+ */
+export const AUTH_BFF_BASE_URL = new InjectionToken<string>('AUTH_BFF_BASE_URL');
+
+/**
+ * Indirection over `window.location.assign(...)` used by `login()`
+ * and `logout()`. Injecting the navigator lets specs assert the
+ * outbound URL without having to redefine `window.location` (which
+ * jsdom resists across multiple tests in the same file).
+ *
+ * The default implementation in `provideAuth()` calls
+ * `window.location.assign(url)`. Tests can override with a `vi.fn()`.
+ */
+export const AUTH_NAVIGATOR = new InjectionToken<(url: string) => void>('AUTH_NAVIGATOR', {
+  providedIn: 'root',
+  factory: () => (url: string) => window.location.assign(url),
+});

libs/feature/auth/src/lib/auth.service.spec.ts

@@ -0,0 +1,125 @@
+import { provideHttpClient } from '@angular/common/http';
+import { HttpTestingController, provideHttpClientTesting } from '@angular/common/http/testing';
+import { TestBed } from '@angular/core/testing';
+import { AUTH_BFF_BASE_URL, AUTH_NAVIGATOR } from './auth.config';
+import { AuthService } from './auth.service';
+import type { CurrentUser } from './auth.types';
+
+const BFF_BASE = 'http://bff.test/api';
+const ME_URL = `${BFF_BASE}/auth/me`;
+
+const USER: CurrentUser = {
+  oid: 'user-oid',
+  tid: 'tenant-id',
+  username: 'jane.doe@apf.example',
+  displayName: 'Jane Doe',
+};
+
+interface Fixture {
+  service: AuthService;
+  http: HttpTestingController;
+  navigate: ReturnType<typeof vi.fn>;
+}
+
+function setup(): Fixture {
+  const navigate = vi.fn();
+  TestBed.configureTestingModule({
+    providers: [
+      provideHttpClient(),
+      provideHttpClientTesting(),
+      { provide: AUTH_BFF_BASE_URL, useValue: BFF_BASE },
+      { provide: AUTH_NAVIGATOR, useValue: navigate },
+      AuthService,
+    ],
+  });
+  const service = TestBed.inject(AuthService);
+  const http = TestBed.inject(HttpTestingController);
+  return { service, http, navigate };
+}
+
+describe('AuthService', () => {
+  afterEach(() => {
+    TestBed.resetTestingModule();
+  });
+
+  describe('bootstrap fetch', () => {
+    it('starts in the loading state before /me resolves', () => {
+      const { service, http } = setup();
+      expect(service.state().kind).toBe('loading');
+      expect(service.isLoading()).toBe(true);
+      expect(service.currentUser()).toBeNull();
+      // Drain the in-flight bootstrap request to keep the controller clean.
+      http.expectOne(ME_URL).flush({}, { status: 401, statusText: 'Unauthorized' });
+    });
+
+    it('transitions to authenticated when /me returns the user', async () => {
+      const { service, http } = setup();
+      http.expectOne(ME_URL).flush(USER);
+      // Let the awaited firstValueFrom commit the state.
+      await Promise.resolve();
+      expect(service.state()).toEqual({ kind: 'authenticated', user: USER });
+      expect(service.currentUser()).toEqual(USER);
+      expect(service.isLoading()).toBe(false);
+    });
+
+    it('transitions to anonymous on 401', async () => {
+      const { service, http } = setup();
+      http
+        .expectOne(ME_URL)
+        .flush({ error: 'unauthenticated' }, { status: 401, statusText: 'Unauthorized' });
+      await Promise.resolve();
+      expect(service.state().kind).toBe('anonymous');
+      expect(service.currentUser()).toBeNull();
+    });
+
+    it('transitions to error on a non-401 failure (network / 5xx / malformed)', async () => {
+      const { service, http } = setup();
+      http.expectOne(ME_URL).flush('boom', { status: 500, statusText: 'Internal Server Error' });
+      await Promise.resolve();
+      expect(service.state().kind).toBe('error');
+      expect(service.currentUser()).toBeNull();
+    });
+  });
+
+  describe('refresh()', () => {
+    it('can be called again after the bootstrap fetch and re-fetches /me', async () => {
+      const { service, http } = setup();
+      http.expectOne(ME_URL).flush(USER);
+      await Promise.resolve();
+      expect(service.state().kind).toBe('authenticated');
+
+      const promise = service.refresh();
+      http
+        .expectOne(ME_URL)
+        .flush({ error: 'unauthenticated' }, { status: 401, statusText: 'Unauthorized' });
+      await promise;
+      expect(service.state().kind).toBe('anonymous');
+    });
+  });
+
+  describe('URL accessors', () => {
+    it('derives me / login / logout URLs from the injected base', () => {
+      const { service, http } = setup();
+      expect(service.meUrl).toBe(`${BFF_BASE}/auth/me`);
+      expect(service.loginUrl).toBe(`${BFF_BASE}/auth/login`);
+      expect(service.logoutUrl).toBe(`${BFF_BASE}/auth/logout`);
+      http.expectOne(ME_URL).flush({}, { status: 401, statusText: 'Unauthorized' });
+    });
+  });
+
+  describe('login() / logout()', () => {
+    it('navigates to /auth/login via AUTH_NAVIGATOR', () => {
+      const { service, http, navigate } = setup();
+      service.login();
+      expect(navigate).toHaveBeenCalledWith(`${BFF_BASE}/auth/login`);
+      http.expectOne(ME_URL).flush({}, { status: 401, statusText: 'Unauthorized' });
+    });
+
+    it('navigates to /auth/logout via AUTH_NAVIGATOR', () => {
+      const { service, http, navigate } = setup();
+      service.logout();
+      expect(navigate).toHaveBeenCalledWith(`${BFF_BASE}/auth/logout`);
+      http.expectOne(ME_URL).flush({}, { status: 401, statusText: 'Unauthorized' });
+    });
+  });
+});

libs/feature/auth/src/lib/auth.service.ts

@@ -0,0 +1,114 @@
+import { HttpClient, HttpErrorResponse } from '@angular/common/http';
+import { Injectable, computed, inject, signal } from '@angular/core';
+import { firstValueFrom } from 'rxjs';
+import { AUTH_BFF_BASE_URL, AUTH_NAVIGATOR } from './auth.config';
+import type { AuthState, CurrentUser } from './auth.types';
+
+/**
+ * SPA-side authentication state, sourced from the BFF's
+ * `GET /api/auth/me` (ADR-0009 / ADR-0010). Acts as the single point
+ * of truth for "is the user signed in?" — every consumer (header
+ * widget, future route guards, downstream API gates) reads from the
+ * `state` / `currentUser` signals.
+ *
+ * Auto-bootstraps on first injection: the constructor fires an
+ * unawaited `refresh()`, so consuming components see `{kind:
+ * 'loading'}` briefly, then either `authenticated` or `anonymous`.
+ *
+ * `login()` and `logout()` perform full-page navigations to the BFF
+ * routes — the SPA never holds tokens (per ADR-0009), so a browser
+ * redirect through the Entra round-trip is the canonical path.
+ */
+@Injectable({ providedIn: 'root' })
+export class AuthService {
+  private readonly http = inject(HttpClient);
+  private readonly bffBaseUrl = inject(AUTH_BFF_BASE_URL);
+  private readonly navigate = inject(AUTH_NAVIGATOR);
+
+  private readonly _state = signal<AuthState>({ kind: 'loading' });
+
+  readonly state = this._state.asReadonly();
+
+  /**
+   * Convenience: the user payload when authenticated, `null`
+   * otherwise. Lets templates write `@if (currentUser(); as user)`
+   * without unwrapping the discriminated state by hand.
+   */
+  readonly currentUser = computed<CurrentUser | null>(() => {
+    const s = this._state();
+    return s.kind === 'authenticated' ? s.user : null;
+  });
+
+  /** True only while the very first /me round-trip is in flight. */
+  readonly isLoading = computed(() => this._state().kind === 'loading');
+
+  constructor() {
+    // Fire-and-forget so the constructor stays synchronous —
+    // Angular DI runs `providedIn: 'root'` services on first inject,
+    // which happens during app boot; awaiting here would push the
+    // first render behind the network round-trip.
+    void this.refresh();
+  }
+
+  /**
+   * Re-fetch `/auth/me`. Called automatically on first injection;
+   * consumers can call it again to refresh after a flow that may
+   * have changed the session (login redirect return, MFA step-up).
+   * Resolves once the new state is committed.
+   */
+  async refresh(): Promise<void> {
+    try {
+      const user = await firstValueFrom(this.http.get<CurrentUser>(this.meUrl));
+      this._state.set({ kind: 'authenticated', user });
+    } catch (err) {
+      this._state.set(toErrorState(err));
+    }
+  }
+
+  /**
+   * Initiate sign-in by navigating to the BFF's `/auth/login`. The
+   * BFF builds the Entra authorize URL and 302s the browser; the
+   * round-trip lands on `/auth/callback` which writes the session
+   * and redirects back to the SPA.
+   *
+   * The navigation goes through the injected {@link AUTH_NAVIGATOR}
+   * function — `window.location.assign` in production, a `vi.fn()`
+   * in specs.
+   */
+  login(): void {
+    this.navigate(this.loginUrl);
+  }
+
+  /**
+   * Initiate sign-out by navigating to the BFF's `/auth/logout`,
+   * which destroys the session, clears the cookie, and 302s through
+   * Entra's RP-initiated logout — single sign-out per ADR-0009.
+   */
+  logout(): void {
+    this.navigate(this.logoutUrl);
+  }
+
+  get meUrl(): string {
+    return `${this.bffBaseUrl}/auth/me`;
+  }
+
+  get loginUrl(): string {
+    return `${this.bffBaseUrl}/auth/login`;
+  }
+
+  get logoutUrl(): string {
+    return `${this.bffBaseUrl}/auth/logout`;
+  }
+}
+
+function toErrorState(err: unknown): AuthState {
+  // The BFF returns 401 with `{error: 'unauthenticated'}` when no
+  // session is on the request. Anything else (network failure,
+  // 5xx, malformed response) lands in the explicit `error` state so
+  // the UI can distinguish "please sign in" from "can't reach the
+  // server right now".
+  if (err instanceof HttpErrorResponse && err.status === 401) {
+    return { kind: 'anonymous' };
+  }
+  return { kind: 'error' };
+}

libs/feature/auth/src/lib/auth.types.ts

@@ -0,0 +1,30 @@
+/**
+ * Curated SPA-facing view of the session user, served by the BFF at
+ * `GET /api/auth/me`. Mirrors the `PublicUser` shape the BFF returns
+ * (apps/portal-bff/src/auth/auth.controller.ts) — internal claims
+ * like `amr` stay server-side and never reach the SPA.
+ */
+export interface CurrentUser {
+  readonly oid: string;
+  readonly tid: string;
+  readonly username: string;
+  readonly displayName: string;
+}
+
+/**
+ * The four observable states of authentication on the SPA, modelled
+ * as a discriminated union so consumers can `switch` on `kind` and
+ * the type narrows automatically.
+ *
+ *   - `loading` — first /me call hasn't returned yet.
+ *   - `anonymous` — BFF answered 401, no session cookie or expired.
+ *   - `authenticated` — BFF returned the user payload.
+ *   - `error` — network failure, 5xx, or unexpected shape. Distinct
+ *     from `anonymous` so the UI can surface a different message
+ *     ("can't reach server" vs. "please sign in").
+ */
+export type AuthState =
+  | { readonly kind: 'loading' }
+  | { readonly kind: 'anonymous' }
+  | { readonly kind: 'authenticated'; readonly user: CurrentUser }
+  | { readonly kind: 'error' };

libs/feature/auth/src/lib/feature-auth/feature-auth.html

@@ -1 +0,0 @@
-<p>FeatureAuth works!</p>

libs/feature/auth/src/lib/feature-auth/feature-auth.spec.ts

@@ -1,21 +0,0 @@
-import { ComponentFixture, TestBed } from '@angular/core/testing';
-import { FeatureAuth } from './feature-auth';
-
-describe('FeatureAuth', () => {
-  let component: FeatureAuth;
-  let fixture: ComponentFixture<FeatureAuth>;
-
-  beforeEach(async () => {
-    await TestBed.configureTestingModule({
-      imports: [FeatureAuth],
-    }).compileComponents();
-
-    fixture = TestBed.createComponent(FeatureAuth);
-    component = fixture.componentInstance;
-    await fixture.whenStable();
-  });
-
-  it('should create', () => {
-    expect(component).toBeTruthy();
-  });
-});

libs/feature/auth/src/lib/feature-auth/feature-auth.ts

@@ -1,9 +0,0 @@
-import { Component } from '@angular/core';
-
-@Component({
-  selector: 'lib-feature-auth',
-  imports: [],
-  templateUrl: './feature-auth.html',
-  styleUrl: './feature-auth.css',
-})
-export class FeatureAuth {}