Integrate email notifications into signup and login (#38)

frontend/app/lib/main.dart

@@ -20,13 +20,19 @@ import 'generated/i18n/app_localizations.dart';
 Future<void> main() async {
   final binding = WidgetsFlutterBinding.ensureInitialized();
   final locale = await LocaleProvider.load(binding.platformDispatcher.locales);
-  runApp(SxchngeApp(localeProvider: locale));
+  const apiUrl = String.fromEnvironment('SXCHNGE_API_URL');
+  const clientId = String.fromEnvironment('SXCHNGE_CLIENT_ID');
+  final backend = apiUrl.isEmpty
+      ? null
+      : BackendAuthServices(baseUri: Uri.parse(apiUrl), clientId: clientId);
+  runApp(SxchngeApp(localeProvider: locale, backend: backend));
 }
 
 class SxchngeApp extends StatefulWidget {
   const SxchngeApp({
     super.key,
     this.localeProvider,
+    this.backend,
     this.analyticsService,
     this.identityService,
     this.limitsService,
@@ -38,6 +44,7 @@ class SxchngeApp extends StatefulWidget {
     this.verificationService = const DummyVerificationService(),
   });
   final LocaleProvider? localeProvider;
+  final BackendAuthServices? backend;
   final AnalyticsService? analyticsService;
   final IdentityService? identityService;
   final LimitsService? limitsService;
@@ -56,7 +63,8 @@ class _SxchngeAppState extends State<SxchngeApp> {
   late final _locale = widget.localeProvider ?? LocaleProvider();
 
   late final _analytics = widget.analyticsService ?? DummyAnalyticsService();
-  late final _factors = widget.twoFactorService ?? DummyTwoFactorService();
+  late final _factors =
+      widget.backend ?? widget.twoFactorService ?? DummyTwoFactorService();
   late final _security = SecurityProvider(_factors, _analytics);
   late final _identity = widget.identityService ?? DummyIdentityService();
   late final _walletService =
@@ -79,12 +87,18 @@ class _SxchngeAppState extends State<SxchngeApp> {
   late final _journeys = JourneyRecorder(_analytics);
   late final _services = InstrumentedAuthServices(
     recorder: _journeys,
-    loginService: GuardedLoginService(widget.loginService, _factors),
-    signupService: widget.signupService,
-    verificationService: widget.verificationService,
+    loginService: GuardedLoginService(
+      widget.backend ?? widget.loginService,
+      _factors,
+    ),
+    signupService: widget.backend ?? widget.signupService,
+    verificationService: widget.backend ?? widget.verificationService,
   );
-  late final _router = createAppRouter()
-    ..routeInformationProvider.addListener(_routeChanged);
+  late final _router = createAppRouter(
+    authenticated: widget.backend == null
+        ? null
+        : () => widget.backend!.session != null,
+  )..routeInformationProvider.addListener(_routeChanged);
   String _previousPath = '/';
 
   @override
@@ -109,6 +123,7 @@ class _SxchngeAppState extends State<SxchngeApp> {
     _wallet.dispose();
     _security.dispose();
     _locale.dispose();
+    widget.backend?.close();
     super.dispose();
   }