Add reusable two-factor verification for login and money operations (#32)

frontend/packages/sxchnge_auth/lib/src/services/instrumented.dart

@@ -1,14 +1,16 @@
 import 'package:sxchnge_analytics/sxchnge_analytics.dart';
 
 import '../models/auth.dart';
+import '../models/two_factor.dart';
 import '../models/verification.dart';
 import 'contracts.dart';
+import 'guarded_login.dart';
 import 'verification.dart';
 
 /// Decorates domain services, so widget rebuilds never produce analytics events.
 class InstrumentedAuthServices
     implements
-        LoginService,
+        PendingLoginService,
         SignupService,
         VerificationService,
         SimulationInfo {
@@ -33,6 +35,7 @@ class InstrumentedAuthServices
     Future<T> Function() action,
     bool Function(T) simulated, {
     bool terminal = false,
+    bool Function(T)? terminalWhen,
     bool onboarding = false,
     bool simulation = false,
   }) async {
@@ -47,7 +50,7 @@ class InstrumentedAuthServices
       recorder.finish(
         operation,
         simulated: simulated(result),
-        terminal: terminal,
+        terminal: terminalWhen?.call(result) ?? terminal,
       );
       return result;
     } catch (error) {
@@ -57,12 +60,17 @@ class InstrumentedAuthServices
           AuthError.emailInUse => JourneyFailure.emailInUse,
           AuthError.unavailable => JourneyFailure.unavailable,
           AuthError.unexpected => JourneyFailure.unexpected,
+          AuthError.factorLocked ||
+          AuthError.factorCooldown => JourneyFailure.unavailable,
+          AuthError.factorRequired => JourneyFailure.invalid,
         },
         VerificationException(code: final code) => switch (code) {
           VerificationError.expired => JourneyFailure.expired,
           VerificationError.invalid => JourneyFailure.invalid,
           VerificationError.internal => JourneyFailure.internal,
         },
+        FactorException(code: FactorError.expired) => JourneyFailure.expired,
+        FactorException() => JourneyFailure.unavailable,
         _ => JourneyFailure.unexpected,
       };
       recorder.finish(operation, failure: failure);
@@ -79,6 +87,23 @@ class InstrumentedAuthServices
     JourneyStep.login,
     () => loginService.login(request),
     (r) => r.isSimulated,
+    terminalWhen: (r) => r.challenge == null,
+    simulation: _simulation(loginService),
+  );
+  @override
+  Future<AuthResult> completeLogin(
+    FactorChallenge challenge,
+    FactorGrant grant,
+  ) => _run(
+    JourneyKind.login,
+    JourneyStep.login,
+    () {
+      final service = loginService;
+      if (service is! PendingLoginService)
+        throw const AuthException(AuthError.unavailable);
+      return service.completeLogin(challenge, grant);
+    },
+    (r) => r.isSimulated,
     terminal: true,
     simulation: _simulation(loginService),
   );