The root widget which you are calling Authentication is the app.
In pubspec.yaml add two dependencies
provider: ^4.0.3
shared_preferences: ^0.5.6+1
Similar to the example, I wrote on Flutter provider state management, logout concept.
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:shared_preferences/shared_preferences.dart';
// If successful, returns a token. Otherwise throws an error.
typedef Future<String> SignIn({
@required final String username,
@required final String password,
});
// If successful, returns void. Otherwise throws an error.
typedef Future<void> SignOut({
@required final String token,
});
// ----------------------------------------------------------------------------
class Session with ChangeNotifier {
String _token; // can be null
final SignIn _signIn;
final SignOut _signOut;
Session({
@required String token,
@required SignIn signIn,
@required SignOut signOut,
}) : assert(signIn != null),
assert(signOut != null),
this._token = token,
this._signIn = signIn,
this._signOut = signOut;
Future<void> signIn({
@required final String username,
@required final String password,
}) async {
assert(username != null);
assert(password != null);
final String token = await this._signIn(
username: username,
password: password,
);
this._token = token;
this.notifyListeners();
}
Future<void> signOut() async {
await this._signOut(token: this._token);
this._token = null;
this.notifyListeners();
}
bool get isAuthenticated {
return (this._token != null);
}
}
// ----------------------------------------------------------------------------
Future<void> main() async {
// The app would load and present an error message on screen to add the following line.
// https://github.com/flutter/flutter/issues/39620
// https://api.flutter.dev/flutter/widgets/WidgetsFlutterBinding/ensureInitialized.html
WidgetsFlutterBinding.ensureInitialized();
// Initialize some local persistence.
// Could be SQLite or somewhere encrypted.
SharedPreferences prefs = await SharedPreferences.getInstance();
final Session session = Session(
token: prefs.getString('token'),
signIn: ({
@required final String username,
@required final String password,
}) async {
assert(username != null);
assert(password != null);
// Contact the server to validate credentials and get token.
await Future.delayed(Duration(milliseconds: 500)); // network delay
if ((username != 'johnsmith') || (password != 'opensesame')) {
throw new Exception("bad username or password");
} else {
final String token = '9djdhy89032jfdhdf70912';
// Store the token locally.
prefs.setString('token', token);
return token;
}
},
signOut: ({@required final String token}) async {
assert(token != null);
// Contact the server to sign out.
await Future.delayed(Duration(milliseconds: 500)); // network delay
// Update the local storage.
prefs.setString('token', null);
},
);
return runApp(
MultiProvider(
providers: [
ChangeNotifierProvider<Session>.value(value: session),
],
child: MyApp(),
),
);
}
class MyApp extends StatelessWidget {
@override
Widget build(final BuildContext context) {
return Consumer<Session>(
builder: (final BuildContext context, final Session session, final Widget child) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(primarySwatch: Colors.blue),
home: session.isAuthenticated ? MyHomePage() : MySignInPage(),
);
},
);
}
}
class MyHomePage extends StatelessWidget {
@override
Widget build(final BuildContext context) {
return Scaffold(
appBar: AppBar(title: const Text("Home [Auth Protected]")),
body: Center(
child: RaisedButton(
child: const Text("Sign Out"),
onPressed: () {
final Session session = Provider.of<Session>(context, listen: false);
session.signOut();
},
),
),
);
}
}
// Of course this would have username and password inputs and a submit button.
class MySignInPage extends StatelessWidget {
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(title: const Text("Sign In")),
body: Center(
child: RaisedButton(
child: const Text("Sign In with johnsmith, opensesame"),
onPressed: () {
final Session session = Provider.of<Session>(context, listen: false);
session.signIn(username: 'johnsmith', password: 'opensesame');
},
),
),
);
}
}
