The Power of Route Guarding in Flutter: Ensuring Secure Authentication Across Mobile and Web

The Importance of Authentication

When building multi-platform applications with Flutter, authentication is a crucial aspect that cannot be overlooked. While Flutter’s mobile-centric approach has led to a wealth of resources and tutorials focused on mobile app development, the same cannot be said for web and desktop development.

The Difference Between Mobile and Web Authentication

In mobile app development, authentication is relatively straightforward. When a user opens the app, you can determine their login status in the main() function and direct them to the appropriate screen. However, things become more complex when it comes to web development. With the ability to navigate using the back and forward buttons in the browser, developers can no longer assume that a user is unable to access certain pages without being authenticated.

The Solution: Route Guarding

To overcome this challenge, we can utilize route guarding to ensure that only authenticated users can access certain pages. By using a route guard, we can elegantly solve this problem and provide a seamless user experience across both mobile and web platforms.

Setting Up a Sample Project

To demonstrate the power of route guarding, let’s create a simple dashboard with both authenticated and unauthenticated screens. We’ll use auto_route for routing, which provides support for deep linking out of the box.

Configuring Routing

// routes/router.dart
import 'package:auto_route/auto_route.dart';

@MaterialAutoRouter(
  replaceInRouteName: 'Page,Route',
  routes: [
    AutoRoute(path: '/', page: DashboardPage),
    AutoRoute(path: '/login', page: LoginPage),
    // Add more routes as needed
  ],
)
class $AppRouter {}

Implementing Route Guarding

To implement route guarding, we’ll create an AuthService to manage authentication data. We’ll then create a RouteGuard class that attaches a listener to the AuthService and triggers whenever there’s a change in authentication state. This ensures that our route guard always has access to the latest authentication data.

// auth/auth_service.dart
class AuthService with ChangeNotifier {
  bool _isLoggedIn = false;

  bool get isLoggedIn => _isLoggedIn;

  void login() {
    _isLoggedIn = true;
    notifyListeners();
  }

  void logout() {
    _isLoggedIn = false;
    notifyListeners();
  }
}

// guards/route_guard.dart
class RouteGuard extends AutoRouteGuard {
  final AuthService _authService;

  RouteGuard(this._authService) {
    _authService.addListener(_onAuthStateChanged);
  }

  @override
  void dispose() {
    _authService.removeListener(_onAuthStateChanged);
    super.dispose();
  }

  bool _onAuthStateChanged() {
    // Redirect to login screen if not authenticated
    if (!_authService.isLoggedIn) {
      // Navigate to login screen
      return false;
    }
    return true;
  }
}

Putting it all Together

With our route guard in place, we can now navigate to our login screen if a user is not authenticated. Once logged in, we’ll redirect them to the original page they were trying to access. We’ll also use the router.removeLast() method to remove the login screen from our navigation stack, ensuring that the user is not taken back to the login screen when pressing the back button.

The Result: Seamless Authentication Across Mobile and Web

By using route guarding, we’ve successfully ensured secure authentication across both mobile and web platforms. Our solution is elegant, scalable, and easy to maintain. Whether you’re building a complex enterprise application or a simple dashboard, route guarding is an essential tool to have in your toolkit.

• Scalable: Route guarding allows you to easily manage complex navigation flows.
• Easy to maintain: With a clear separation of concerns, your code becomes easier to understand and maintain.
• Seamless user experience: Route guarding ensures that users are seamlessly redirected to the correct page, regardless of their authentication status.