Flutter : How to keep user logged in and make logout

I am getting the csrf token and printing the response data in console but how to keep user logged in using the response data.I am making login using the status code i.e., if status code is 200 then move to login after that I want to keep user logged in and log out only when user wants to log out

I have seen lot of examples but none are helping in my case.

In my case i am using th csrf token and unable to keep it logged in, and i have also used login form.

LoginPage.dart

import 'dart:io';

import 'package:cookie_jar/cookie_jar.dart';
import 'package:dio/dio.dart';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:jignasa/home_screen.dart';
import 'package:jignasa/logindata.dart';
import 'package:path_provider/path_provider.dart';


class LoginPage extends StatefulWidget {
  static String tag = 'login-page';
  @override
  _LoginPageState createState() => new _LoginPageState();
}

class _LoginPageState extends State<LoginPage> {
  final GlobalKey<FormState> _formKey = GlobalKey<FormState>();
  LoginRequestData _loginData = LoginRequestData();


  bool _validate = false;
  bool _obscureText = true;
  var username, password;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      // backgroundColor: Colors.white,
      body: SingleChildScrollView(
        child: Container(
          color: Colors.lightGreen[500],
          child: Column(
            children: <Widget>[
              Center(
                child: Container(
                  width: MediaQuery
                      .of(context)
                      .size
                      .width,
                  height: MediaQuery
                      .of(context)
                      .size
                      .height / 2.5,
                  decoration: BoxDecoration(
                      gradient: LinearGradient(
                        // begin: Alignment.topCenter,
                        // end: Alignment.bottomCenter,
                          colors: [
                            Color(0xFFFFFFFF),
                            Color(0xFFFFFFFF),
                          ]
                      ),
                      borderRadius: BorderRadius.only(
                          bottomLeft: Radius.circular(90)
                      )
                  ),
                  child: Column(
                    mainAxisAlignment: MainAxisAlignment.center,
                    children: <Widget>[
                      Align(
                        alignment: Alignment.center,
                        child: Image.asset('images/ic_launcher1.png'),
                      ),
                    ],
                  ),
                ),
              ),
              Center(
                  child: SingleChildScrollView(
                    child: new Form(
                      key: _formKey,
                      autovalidate: _validate,
                      child: _getFormUI(),
                    ),
                  )
              )

            ],
          ),
        ),
      ),
    );
  }

  Widget _getFormUI() {
    return new Column(
      children: <Widget>[
        SizedBox(height: 24.0),
        Center(
          child: Text('Login',
            style: TextStyle(fontSize: 25,
                fontWeight: FontWeight.bold,
                color: Colors.white),),
        ),
        new SizedBox(height: 25.0),
        new TextFormField(
          keyboardType: TextInputType.emailAddress,
          autofocus: false,
          decoration: InputDecoration(
            hintText: 'Username',
            contentPadding: EdgeInsets.fromLTRB(20.0, 15.0, 20.0, 15.0),
            border:
            OutlineInputBorder(borderRadius: BorderRadius.circular(32.0)),
          ),
          validator: _validateName,
          onSaved: (value) {
            _loginData.username = value;
          },
        ),
        new SizedBox(height: 8.0),
        new TextFormField(
            autofocus: false,
            obscureText: _obscureText,
            keyboardType: TextInputType.text,
            decoration: InputDecoration(
              hintText: 'Password',
              contentPadding: EdgeInsets.fromLTRB(20.0, 10.0, 20.0, 10.0),
              border:
              OutlineInputBorder(borderRadius: BorderRadius.circular(24.0)),
              suffixIcon: GestureDetector(
                child: Icon(
                  _obscureText ? Icons.visibility : Icons.visibility_off,
                  semanticLabel:
                  _obscureText ? 'show password' : 'hide password',
                ),
              ),
            ),
            validator: _validatePassword,
            onSaved: (String value) {
              _loginData.password = value;
            }
        ),
        new SizedBox(height: 15.0),
        new Padding(
          padding: EdgeInsets.symmetric(vertical: 16.0),
          child: RaisedButton(
            shape: RoundedRectangleBorder(
              borderRadius: BorderRadius.circular(24),
            ),
            onPressed: () {
              _submit();
//              Navigator.of(context).pushReplacementNamed('/home');
            },
            padding: EdgeInsets.all(12),
            color: Colors.black54,
            child: Text('Log In', style: TextStyle(color: Colors.white)),
          ),
        ),
        new FlatButton(
          child: Text(
            'Forgot password?',
            style: TextStyle(color: Colors.black54),
          ),
          onPressed: () {},
        ),
        new FlatButton(
          onPressed: _sendToRegisterPage,
          child: Text('Not a member? Sign up now',
              style: TextStyle(color: Colors.black54)),
        ),
        Text(''),
        Text(''),
        Text(''),
      ],
    );
  }

  _sendToRegisterPage() {
    Navigator.push(
      context,
      MaterialPageRoute(builder: (context) => HomeScreen()),
    );
  }

  String _validateName(String value) {
    if (value.isEmpty) {
      return "Username is Required";
    } else {
      username = value.toString();
    }
  }

  String _validatePassword(String value) {
    if (value.isEmpty) {
      return "Password is Required";
    } else {
      password = value.toString();
    }
  }

  _submit() {
    if (_formKey.currentState.validate()) {
      _formKey.currentState.save();
      print("Username ${_loginData.username}");
      print("Password ${_loginData.password}");
      return SessionId();
    } else {
      setState(() {
        bool _validate = false;
      });
    }
  }


  final Dio _dio = Dio();
  PersistCookieJar persistentCookies;
  final String url = "https://www.xxxx.in/rest/user/login.json";

  Future<String> get _localPath async {
    final directory = await getApplicationDocumentsDirectory();
    print(directory.path);
    return directory.path;
  }

  Future<Directory> get _localCoookieDirectory async {
    final path = await _localPath;
    final Directory dir = new Directory('$path/cookies');
    await dir.create();
    print(dir);
    return dir;
  }

  Future<String> getCsrftoken() async{
    try {
      String csrfTokenValue;
      final Directory dir = await _localCoookieDirectory;
      final cookiePath = dir.path;
      persistentCookies = new PersistCookieJar(dir: '$cookiePath');
      persistentCookies.deleteAll(); //clearing any existing cookies for a fresh start
      _dio.interceptors.add(
          CookieManager(persistentCookies) //this sets up _dio to persist cookies throughout subsequent requests
      );
      _dio.options = new BaseOptions(
        baseUrl: url,
        contentType: ContentType.json,
        responseType: ResponseType.plain,
        // connectTimeout: 5000,
        // receiveTimeout: 100000,
        headers: {
          HttpHeaders.userAgentHeader: "dio",
          "Connection": "keep-alive",
        },
      ); //BaseOptions will be persisted throughout subsequent requests made with _dio
      _dio.interceptors.add(
          InterceptorsWrapper(
              onResponse:(Response response) {
                List<Cookie> cookies = persistentCookies.loadForRequest(Uri.parse(url));
                csrfTokenValue = cookies.firstWhere((c) => c.name == 'csrftoken', orElse: () => null)?.value;
                if (csrfTokenValue != null) {
                  _dio.options.headers['X-CSRF-TOKEN'] = csrfTokenValue; //setting the csrftoken from the response in the headers
                }
                print(response);
                return response;
              }
          )
      );
      await _dio.get("https://www.xxxx.in/rest/user/login.json");
      print(csrfTokenValue);
      return csrfTokenValue;
    } catch (error, stacktrace) {
      print(error);
//      print("Exception occured: $error stackTrace: $stacktrace");
      return null;
    }
  }

   SessionId() async {
     try {
       final csrf = await getCsrftoken();
       FormData formData = new FormData.from({
         "username": "${_loginData.username}",
         "password": "${_loginData.password}",
         "csrfmiddlewaretoken" : '$csrf'
       });
       Options optionData = new Options(
         contentType: ContentType.parse("application/json"),
       );
       Response response = await _dio.post("https://www.xxxx.in/rest/user/login.json", data: formData, options: optionData);
       print("StatusCode:${response.statusCode}");
      //  print(response.data);
       if (response.statusCode == 200){
         return Navigator.of(context).pushReplacement(MaterialPageRoute(
             builder: (context) => HomeScreen(),
         ));
       }
       else{
         throw Exception();
       }
     } on DioError catch(e) {
       if(e.response != null) {
         print( e.response.statusCode.toString() + " " + e.response.statusMessage);
         print(e.response.data);
         print(e.response.headers);
         print(e.response.request);
       } else{
         print(e.request);
         print(e.message);
       }
     }
     catch (error, stacktrace) {
       print("Exception occured: $error stackTrace: $stacktrace");
       return null;
     }
   }
}

You can make an entry in Shared preference after getting response code 200 from api.

 SharedPreferences prefs = await SharedPreferences.getInstance();
 prefs?.setBool("isLoggedIn", true);

then you can navigate user after checking status from shared preference

Future<void> main() async {
  SharedPreferences prefs = await SharedPreferences.getInstance();
  var status = prefs.getBool('isLoggedIn') ?? false;
  print(status);
  runApp(MaterialApp(home: status == true ? Login() : Home()));
}

Update :-

Another way of doing it is you can also add your logic into splash screen and splash screen should be entry point in your app

class SplashScreen extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    // TODO: implement createState
    return _SplashScreenState();
  }
}

class _SplashScreenState extends State<SplashScreen> {
  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    startTimer();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
        decoration: BoxDecoration(
          image: DecorationImage(
              image: AssetImage("assets/images/clinician_splash.png"),
              fit: BoxFit.cover),
        ),
      ),
    );
  }

  void startTimer() {
    Timer(Duration(seconds: 3), () {
      navigateUser(); //It will redirect  after 3 seconds
    });
  }

  void navigateUser() async{
    SharedPreferences prefs = await SharedPreferences.getInstance();
    var status = prefs.getBool('isLoggedIn') ?? false;
    print(status);
    if (status) {
      Navigation.pushReplacement(context, "/Home");
    } else {
      Navigation.pushReplacement(context, "/Login");
    }
  }
}

For logout add below functionality in onPress event of logout button :

void logoutUser(){
SharedPreferences prefs = await SharedPreferences.getInstance();
prefs?.clear() 
 Navigator.pushAndRemoveUntil(
      context, 
      ModalRoute.withName("/SplashScreen"), 
     ModalRoute.withName("/Home")
    );
}

For security :-

Here in example I have used SharedPreferences which is not secure.for security you can change SharedPreferences to flutter_secure_storage.

https://pub.dev/packages/flutter_secure_storage#-readme-tab-