fix: BAD_DECRYPT Exception on invalid cipher

packages/smooth_app/lib/data_models/user_management_provider.dart

@@ -1,4 +1,6 @@
-import 'package:flutter/cupertino.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
+import 'package:flutter_gen/gen_l10n/app_localizations.dart';
 import 'package:openfoodfacts/openfoodfacts.dart';
 import 'package:openfoodfacts/utils/OpenFoodAPIConfiguration.dart';
 import 'package:smooth_app/database/dao_secured_string.dart';
@@ -38,9 +40,25 @@ class UserManagementProvider with ChangeNotifier {
   }
 
   /// Mounts already stored credentials, called at app startup
-  Future<void> mountCredentials() async {
-    final String? userId = await DaoSecuredString.get(_USER_ID);
-    final String? password = await DaoSecuredString.get(_PASSWORD);
+  Future<void> mountCredentials(BuildContext context) async {
+    String? userId;
+    String? password;
+
+    try {
+      userId = await DaoSecuredString.get(_USER_ID);
+      password = await DaoSecuredString.get(_PASSWORD);
+    } on PlatformException {
+      /// Decrypting the values can go wrong if, for example, the app was
+      /// manually overwritten from an external apk.
+      DaoSecuredString.remove(key: _USER_ID);
+      DaoSecuredString.remove(key: _PASSWORD);
+      ScaffoldMessenger.of(context).showSnackBar(
+        SnackBar(
+          content: Text(AppLocalizations.of(context)!.you_have_been_logged_out),
+          duration: const Duration(seconds: 2),
+        ),
+      );
+    }
 
     if (userId == null || password == null) {
       _finishedLoading = true;

packages/smooth_app/lib/l10n/app_en.arb

@@ -888,5 +888,9 @@
     "user_list_name_error_same": "That is the same name",
     "@user_list_name_error_same": {
         "description": "Validation error about the renamed name that is the same as the initial list name"
+    },
+    "you_have_been_logged_out": "You have been logged out",
+    "@you_have_been_logged_out": {
+        "description": "Hint when the user got automatically logged out for example for security reasons"
     }
 }

packages/smooth_app/lib/main.dart

@@ -227,8 +227,6 @@ class SmoothAppGetLanguage extends StatelessWidget {
     final LocalDatabase _localDatabase = context.read<LocalDatabase>();
     AnalyticsHelper.trackStart(_localDatabase, context);
 
-    context.read<UserManagementProvider>().mountCredentials();
-
     return appWidget;
   }
 }

packages/smooth_app/lib/pages/page_manager.dart

@@ -1,5 +1,7 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_gen/gen_l10n/app_localizations.dart';
+import 'package:provider/provider.dart';
+import 'package:smooth_app/data_models/user_management_provider.dart';
 import 'package:smooth_app/pages/scan/inherited_data_manager.dart';
 import 'package:smooth_app/widgets/tab_navigator.dart';
 
@@ -58,6 +60,11 @@ class PageManagerState extends State<PageManager> {
       _buildOffstageNavigator(BottomNavigationTab.History),
     ];
 
+    // Mounting the user credentials, needs to be done after build of the first
+    // Scaffold to be able to show a optional error Snackbar
+    WidgetsBinding.instance?.addPostFrameCallback((_) =>
+        context.read<UserManagementProvider>().mountCredentials(context));
+
     final ThemeData themeData = Theme.of(context);
     final bool brightnessCheck = themeData.brightness == Brightness.light;
     return WillPopScope(