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

frontend/app/lib/workspace/transfer.dart

@@ -6,8 +6,12 @@ import 'package:go_router/go_router.dart';
 
 import 'package:provider/provider.dart';
 
+import 'package:sxchnge_auth/sxchnge_auth.dart';
+
 import 'package:sxchnge_wallet/sxchnge_wallet.dart';
 
+import '../security/challenge.dart';
+
 import 'copy.dart';
 import 'summary.dart';
 
@@ -64,6 +68,25 @@ class TransferPageState extends State<TransferPage> {
     }
   }
 
+  Future<void> _confirm() async {
+    final p = _provider;
+    final challenge = await p.challenge();
+    if (!mounted || p.factorError != null || p.error != null) return;
+    FactorGrant? grant;
+    if (challenge != null) {
+      grant = await verifyFactor(
+        context,
+        challenge: challenge,
+        service: p.wallet.factors!,
+        recorder: p.recorder,
+        journey: p.journey,
+        summary: TransferSummary(quote: p.quote!),
+      );
+      if (!mounted || grant == null) return;
+    }
+    await p.submit(approval: grant);
+  }
+
   Future<bool> allowExit() async {
     if (_provider.result != null) return true;
     if (_provider.busy || _provider.uncertain) return false;
@@ -163,6 +186,17 @@ class TransferPageState extends State<TransferPage> {
                             ),
                           ),
                         ),
+                      if (p.factorError != null)
+                        Padding(
+                          padding: const EdgeInsets.only(bottom: 16),
+                          child: Semantics(
+                            liveRegion: true,
+                            child: Text(
+                              factorErrorText(l, p.factorError!),
+                              style: TextStyle(color: t.colorScheme.error),
+                            ),
+                          ),
+                        ),
                       if (p.noSubmission) Text(l.wNoSubmission),
                       if (p.uncertain) ...[
                         Text(l.wUncertain),
@@ -183,7 +217,7 @@ class TransferPageState extends State<TransferPage> {
                         else
                           FilledButton(
                             key: const ValueKey('transfer-confirm'),
-                            onPressed: p.busy ? null : p.submit,
+                            onPressed: p.busy ? null : _confirm,
                             child: Text(l.wConfirm),
                           ),
                         TextButton(