Auth data resets whenever App is rebuild in Flutter - flutter

Question

I have an Auth method setup that extends ChangeNotifier to give login and store tokens and other details.
and in my main.dart file I am calling a multi provider to get all providers, inside multi provider I have a Consumer as a child which decides which page to call as default. i.e if auth.isAuth returns true then MainPage.dart will be called or AuthScreen.dart.
Login works fine and everything else works fine.
But the issue which I am facing is, Whenever is reload or rebuild my application the auth data becomes null.
Any kind of help will be appreciated. Thanks in Advance.
main.dart
#override
Widget build(BuildContext context) {
return MultiProvider(
providers: [
ChangeNotifierProvider.value(
value: Auth(),
),
ChangeNotifierProvider.value(
value: Cart(),
),
ChangeNotifierProvider.value(
value: AddressBook(Auth().token),
),
ChangeNotifierProvider.value(
value: Orders(),
),
],
child: Consumer<Auth>(
builder: (ctx, auth, _) => MaterialApp(
title: 'APP NAME',
theme: ThemeData(
fontFamily: 'Roboto',
primaryColor: Colors.white,
primaryColorDark: Colors.white,
backgroundColor: Colors.white),
home: auth.isAuth ? MainPage() : AuthScreen(),
routes: {
MainPage.routeName: (ctx) => MainPage(),
CartScreen.routeName: (ctx) => CartScreen(),
OrderScreen.routeName: (ctx) => OrderScreen(),
EditAddressScreen.routeName: (ctx) => EditAddressScreen(),
}),
),
);
}
auth.dart
class Auth extends ChangeNotifier {
String _token;
String _refresh_token;
DateTime _expiryDate;
int _userId;
bool get isAuth {
return _token != null;
}
String get token {
if (_expiryDate != null &&
_expiryDate.isAfter(DateTime.now()) &&
_token != null) {
return _token;
}
return null;
}
int get userId {
return _userId;
}
Future<void> _authenticate(String email, String password, String urlSegment) async {
final url = 'http://192.168.1.120:8080/oauth/token';
Map<String, dynamic> body = {'grant_type': 'password', 'username': email, 'password': password};
var parts = [];
parts.add('${Uri.encodeQueryComponent("grant_type")}=${Uri.encodeQueryComponent("password")}');
parts.add('${Uri.encodeQueryComponent("username")}=${Uri.encodeQueryComponent(email)}');
parts.add('${Uri.encodeQueryComponent("password")}=${Uri.encodeQueryComponent(password)}');
var formData = parts.join('&');
try {
final response = await http.post(
url,
body: formData,
headers: {
'content-type': 'application/x-www-form-urlencoded',
'Authorization': 'Basic XXXXXXXXXXXXXXXXXXXXX',
}
);
final responseData = json.decode(response.body);
print(response.statusCode);
if(response.statusCode != 200){
throw HttpException(responseData['error']['error_description']);
}else{
_token = responseData['access_token'];
_userId = responseData['customerId'];
_refresh_token = responseData['refresh_token'];
_expiryDate = DateTime.now().add(
Duration(
seconds: responseData['expires_in'],
),
);
notifyListeners();
}
if (responseData['error'] != null) {
throw HttpException(responseData['error']['error_description']);
}
} catch (error) {
throw error;
}
}
Future<void> signup(String email, String password) async {
return _authenticate(email, password, 'signUp');
}
Future<void> login(String email, String password) async {
return _authenticate(email, password, 'signInWithPassword');
}
}

Answer 1

At the moment it looks like you are storing OAuth tokens in memory, so they are dropped upon every restart, and this provides poor usability.
MOBILE TOKEN STORAGE
OAuth tokens can be saved to secure encrypted storage to improve usability, perhaps using this Flutter library. The encryption used should be private to your app, so that no other app can use the tokens.
STRUCTURING YOUR CODE
I quite like how you've structured your code, where the rest of the app just calls Auth.dart's getToken method when calling a Web API. It looks like your Auth.dart source file needs to do more work to resolve your problem.
EXAMPLE OF MINE
This code is in Swift and uses a different flow, with AppAuth libraries. However, the general design pattern can be applied in any language, including Flutter.
Token Storage Module
OAuth Interface used by the rest of the App
OAuth Implementation uses Token Storage
API Client that calls GetToken
View that Calls an API