Frontend first draft

frontend/pshared/lib/service/secure_storage.dart

@@ -0,0 +1,25 @@
+import 'package:shared_preferences/shared_preferences.dart';
+
+class SecureStorageService {
+  static Future<String?> get(String key) async {
+    final prefs = await SharedPreferences.getInstance();
+    return prefs.getString(key);
+  }
+
+  static Future<void> _setImp(SharedPreferences prefs, String key, String value) async {
+    await prefs.setString(key, value);
+  }
+
+  static Future<void> set(String key, String? value) async {
+    final prefs = await SharedPreferences.getInstance();
+    if (value == null) {
+      return delete(key);  
+    }
+    return _setImp(prefs, key, value);
+  }
+
+  static Future<void> delete(String key) async {
+    final prefs = await SharedPreferences.getInstance();
+    await prefs.remove(key);
+  }
+}