feat(auth): prepare MSAL browser integration

eme-frontend/lib/services/api_client.dart

@@ -37,7 +37,8 @@ class ApiClient {
 
     late final http.Response reponse;
     try {
-      reponse = await http.get(uri, headers: AuthService.requestHeaders());
+      final authHeaders = await AuthService.requestHeaders();
+      reponse = await http.get(uri, headers: authHeaders);
     } catch (_) {
       throw const ApiException(
         "Impossible de joindre le serveur. Vérifiez que le backend est démarré.",
@@ -58,7 +59,8 @@ class ApiClient {
 
     late final http.Response reponse;
     try {
-      reponse = await http.get(uri, headers: AuthService.requestHeaders());
+      final authHeaders = await AuthService.requestHeaders();
+      reponse = await http.get(uri, headers: authHeaders);
     } catch (_) {
       throw const ApiException(
         "Impossible de joindre le serveur. Vérifiez que le backend est démarré.",
@@ -82,12 +84,10 @@ class ApiClient {
 
     late final http.Response reponse;
     try {
+      final authHeaders = await AuthService.requestHeaders();
       reponse = await http.post(
         uri,
-        headers: {
-          ...AuthService.requestHeaders(),
-          "content-type": "application/json",
-        },
+        headers: {...authHeaders, "content-type": "application/json"},
         body: jsonEncode(body),
       );
     } catch (_) {
@@ -107,12 +107,10 @@ class ApiClient {
 
     late final http.Response reponse;
     try {
+      final authHeaders = await AuthService.requestHeaders();
       reponse = await http.patch(
         uri,
-        headers: {
-          ...AuthService.requestHeaders(),
-          "content-type": "application/json",
-        },
+        headers: {...authHeaders, "content-type": "application/json"},
         body: jsonEncode(body),
       );
     } catch (_) {

eme-frontend/lib/services/auth_service.dart

@@ -1,3 +1,5 @@
+import "msal_bridge.dart";
+
 enum AuthenticationMode { demo, azure }
 
 class AuthService {
@@ -17,6 +19,7 @@ class AuthService {
   static const String demoResponsableEmail = "karim.benali@ensup.eu";
 
   static String? _demoEmail;
+  static bool _azureInitialized = false;
 
   static AuthenticationMode get mode {
     return switch (_configuredMode) {
@@ -40,9 +43,31 @@ class AuthService {
     _demoEmail = null;
   }
 
-  static Map<String, String> requestHeaders() {
+  static Future<void> signInWithMicrosoft() async {
+    await _initializeAzure();
+    await MsalBridge.signIn();
+  }
+
+  static Future<bool> hasMicrosoftAccount() async {
+    await _initializeAzure();
+    return MsalBridge.hasAccount();
+  }
+
+  static Future<void> signOut() async {
     if (mode == AuthenticationMode.azure) {
-      throw StateError("La session Microsoft n'est pas encore initialisee.");
+      await _initializeAzure();
+      await MsalBridge.signOut();
+      return;
+    }
+
+    clearSession();
+  }
+
+  static Future<Map<String, String>> requestHeaders() async {
+    if (mode == AuthenticationMode.azure) {
+      await _initializeAzure();
+      final token = await MsalBridge.getAccessToken();
+      return {"authorization": "Bearer $token"};
     }
 
     final email = _demoEmail;
@@ -53,6 +78,28 @@ class AuthService {
     return {"x-user-email": email};
   }
 
+  static Future<void> _initializeAzure() async {
+    if (mode != AuthenticationMode.azure) {
+      throw StateError("MSAL est disponible uniquement en mode Azure.");
+    }
+    if (_azureInitialized) {
+      return;
+    }
+    if (azureTenantId.isEmpty ||
+        azureSpaClientId.isEmpty ||
+        azureApiScope.isEmpty) {
+      throw StateError("La configuration Azure du frontend est incomplete.");
+    }
+
+    await MsalBridge.initialize(
+      tenantId: azureTenantId,
+      clientId: azureSpaClientId,
+      scope: azureApiScope,
+      redirectUri: Uri.base.origin,
+    );
+    _azureInitialized = true;
+  }
+
   static void _ensureDemoMode() {
     if (mode != AuthenticationMode.demo) {
       throw StateError(

eme-frontend/lib/services/msal_bridge.dart

@@ -0,0 +1,56 @@
+import "dart:js_interop";
+
+@JS("emeMsal.initialize")
+external JSPromise<JSAny?> _initialize(
+  JSString tenantId,
+  JSString clientId,
+  JSString scope,
+  JSString redirectUri,
+);
+
+@JS("emeMsal.signIn")
+external JSPromise<JSAny?> _signIn();
+
+@JS("emeMsal.getAccessToken")
+external JSPromise<JSString> _getAccessToken();
+
+@JS("emeMsal.hasAccount")
+external JSBoolean _hasAccount();
+
+@JS("emeMsal.signOut")
+external JSPromise<JSAny?> _signOut();
+
+class MsalBridge {
+  MsalBridge._();
+
+  static Future<void> initialize({
+    required String tenantId,
+    required String clientId,
+    required String scope,
+    required String redirectUri,
+  }) async {
+    await _initialize(
+      tenantId.toJS,
+      clientId.toJS,
+      scope.toJS,
+      redirectUri.toJS,
+    ).toDart;
+  }
+
+  static Future<void> signIn() async {
+    await _signIn().toDart;
+  }
+
+  static Future<String> getAccessToken() async {
+    final token = await _getAccessToken().toDart;
+    return token.toDart;
+  }
+
+  static bool hasAccount() {
+    return _hasAccount().toDart;
+  }
+
+  static Future<void> signOut() async {
+    await _signOut().toDart;
+  }
+}