Add configurable FlutterSecureStorage to FlutterSecureCredentialsStorage

packages/login_client_flutter/README.md

@@ -8,12 +8,33 @@
 ## Usage
 
 ```dart
+// Default usage
 final loginClient = LoginClient(
   credentialsStorage: const FlutterSecureCredentialsStorage(),
   // ...
 );
 ```
 
+### Custom Configuration
+
+You can provide a custom `FlutterSecureStorage` instance to configure platform-specific options:
+
+```dart
+final loginClient = LoginClient(
+  credentialsStorage: const FlutterSecureCredentialsStorage(
+    storage: FlutterSecureStorage(
+      aOptions: AndroidOptions(
+        encryptedSharedPreferences: true,
+      ),
+      iOptions: IOSOptions(
+        accessibility: KeychainAccessibility.first_unlock_this_device,
+      ),
+    ),
+  ),
+  // ...
+);
+```
+
 ## Android `javax.crypto.BadPaddingException`
 
 Exclude Flutter Secure Storage from Android full backup.

packages/login_client_flutter/lib/src/flutter_secure_credentials_storage.dart

@@ -18,14 +18,22 @@ import 'package:login_client/login_client.dart';
 /// A `flutter_secure_storage` implementation of the [CredentialsStorage].
 class FlutterSecureCredentialsStorage implements CredentialsStorage {
   /// Creates the [CredentialsStorage].
-  const FlutterSecureCredentialsStorage();
+  ///
+  /// The optional [storage] parameter allows you to provide a custom
+  /// [FlutterSecureStorage] instance with specific configuration options.
+  /// If not provided, a default instance will be used.
+  const FlutterSecureCredentialsStorage({FlutterSecureStorage? storage})
+      : _storage = storage;
 
   static const _key = 'login_client_flutter_credentials';
-  FlutterSecureStorage get _storage => const FlutterSecureStorage();
+  final FlutterSecureStorage? _storage;
+
+  FlutterSecureStorage get _secureStorage => 
+      _storage ?? const FlutterSecureStorage();
 
   @override
   Future<Credentials?> read() async {
-    final json = await _storage.read(key: _key);
+    final json = await _secureStorage.read(key: _key);
     if (json == null) {
       return null;
     }
@@ -39,11 +47,11 @@ class FlutterSecureCredentialsStorage implements CredentialsStorage {
 
   @override
   Future<void> save(Credentials credentials) {
-    return _storage.write(key: _key, value: credentials.toJson());
+    return _secureStorage.write(key: _key, value: credentials.toJson());
   }
 
   @override
   Future<void> clear() {
-    return _storage.delete(key: _key);
+    return _secureStorage.delete(key: _key);
   }
 }

packages/login_client_flutter/pubspec.yaml

@@ -17,5 +17,7 @@ dependencies:
   login_client: ^3.0.0
 
 dev_dependencies:
+  flutter_test:
+    sdk: flutter
   custom_lint: ^0.6.4
   leancode_lint: ^12.0.0

packages/login_client_flutter/test/flutter_secure_credentials_storage_test.dart

@@ -0,0 +1,72 @@
+import 'package:flutter_secure_storage/flutter_secure_storage.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:login_client_flutter/login_client_flutter.dart';
+import 'package:oauth2/oauth2.dart';
+
+// Mock FlutterSecureStorage for testing
+class MockFlutterSecureStorage extends FlutterSecureStorage {
+  final Map<String, String> _storage = {};
+
+  const MockFlutterSecureStorage() : super();
+
+  @override
+  Future<String?> read({required String key}) async {
+    return _storage[key];
+  }
+
+  @override
+  Future<void> write({required String key, required String value}) async {
+    _storage[key] = value;
+  }
+
+  @override
+  Future<void> delete({required String key}) async {
+    _storage.remove(key);
+  }
+}
+
+void main() {
+  group('FlutterSecureCredentialsStorage', () {
+    test('uses default storage when none provided', () {
+      const storage = FlutterSecureCredentialsStorage();
+
+      // This test ensures the constructor works with no parameters
+      expect(storage, isA<FlutterSecureCredentialsStorage>());
+    });
+
+    test('accepts custom storage instance', () {
+      const customStorage = MockFlutterSecureStorage();
+      const storage = FlutterSecureCredentialsStorage(storage: customStorage);
+
+      // This test ensures the constructor works with custom storage
+      expect(storage, isA<FlutterSecureCredentialsStorage>());
+    });
+
+    test('works with custom storage - read/write/clear operations', () async {
+      const customStorage = MockFlutterSecureStorage();
+      const storage = FlutterSecureCredentialsStorage(storage: customStorage);
+
+      // Test initial read returns null
+      expect(await storage.read(), null);
+
+      // Test saving and reading credentials
+      final credentials = Credentials('test_token');
+      await storage.save(credentials);
+
+      final readCredentials = await storage.read();
+      expect(readCredentials?.accessToken, equals('test_token'));
+
+      // Test clearing
+      await storage.clear();
+      expect(await storage.read(), null);
+    });
+
+    test('maintains backward compatibility with default constructor', () async {
+      // This test verifies that existing code continues to work
+      const storage = FlutterSecureCredentialsStorage();
+
+      // Should be able to perform operations without error
+      expect(storage.read(), completes);
+    });
+  });
+}