add secure storage (not working)

lib/services/authservice.dart

@@ -1,13 +1,16 @@
 import 'package:flutter/foundation.dart';
+import 'package:flutter_secure_storage/flutter_secure_storage.dart';
 import 'package:mileograph_flutter/objects/objects.dart';
 import 'package:mileograph_flutter/services/apiService.dart';
-import 'package:shared_preferences/shared_preferences.dart';
 
 class AuthService extends ChangeNotifier {
   final ApiService api;
   static const _tokenKey = 'auth_token';
   bool _restoring = false;
 
+  // secure storage instance
+  final FlutterSecureStorage _storage = const FlutterSecureStorage();
+
   AuthService({required this.api});
 
   AuthenticatedUserData? _user;
@@ -73,9 +76,10 @@ class AuthService extends ChangeNotifier {
     if (_restoring || _user != null) return;
     _restoring = true;
     try {
-      final prefs = await SharedPreferences.getInstance();
-      final token = prefs.getString(_tokenKey);
+      // read token from secure storage
+      final token = await _storage.read(key: _tokenKey);
       if (token == null || token.isEmpty) return;
+
       final userResponse = await api.get(
         '/users/me',
         headers: {
@@ -83,6 +87,7 @@ class AuthService extends ChangeNotifier {
           'accept': 'application/json',
         },
       );
+
       setLoginData(
         userId: userResponse['user_id'],
         username: userResponse['username'],
@@ -98,13 +103,11 @@ class AuthService extends ChangeNotifier {
   }
 
   Future<void> _persistToken(String token) async {
-    final prefs = await SharedPreferences.getInstance();
-    await prefs.setString(_tokenKey, token);
+    await _storage.write(key: _tokenKey, value: token);
   }
 
   Future<void> _clearToken() async {
-    final prefs = await SharedPreferences.getInstance();
-    await prefs.remove(_tokenKey);
+    await _storage.delete(key: _tokenKey);
   }
 
   Future<void> register({
@@ -126,9 +129,13 @@ class AuthService extends ChangeNotifier {
     await api.postForm('/register', formData);
   }
 
-  void logout() {
+  Future<void> handleTokenExpired() async {
     _user = null;
-    _clearToken();
+    await _clearToken();
     notifyListeners();
   }
+
+  void logout() {
+    handleTokenExpired(); // reuse
+  }
 }