OAuth Acces Token Verification in node.js - node.js

Question

I am working on a flutter app and would want to use facebook and google oauths to authenticate my users. Here is the code on the client side which works perfectly.
import 'package:flutter/material.dart';
import 'package:flutter_facebook_login/flutter_facebook_login.dart';
import 'package:http/http.dart' as http;
import 'dart:convert' as JSON;
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
home: MyHomePage(),
);
}
}
class MyHomePage extends StatefulWidget {
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
bool isLoggedIn = false;
Map userProfile;
final facebookLogin = FacebookLogin();
_loginWithFB() async {
final result = await facebookLogin.logIn(['email']);
switch (result.status) {
case FacebookLoginStatus.loggedIn:
final token = result.accessToken.token;
final graphResponse = await http.get(
'https://graph.facebook.com/v2.12/me?fields=name,picture,email&access_token=${token}');
final profile = JSON.jsonDecode(graphResponse.body);
print(profile);
setState(() {
userProfile = profile;
isLoggedIn = true;
});
break;
case FacebookLoginStatus.cancelledByUser:
setState(() => isLoggedIn = false);
break;
case FacebookLoginStatus.error:
setState(() => isLoggedIn = false);
break;
}
}
_logoutWithFB() {
facebookLogin.logOut().then((value) => setState(() => isLoggedIn = false));
}
#override
Widget build(BuildContext context) {
return Scaffold(
body: Center(
child: isLoggedIn
? Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Image.network(
"http://placehold.it/50x50",
height: 50.0,
width: 50.0,
),
SizedBox(
height: 50.0,
),
OutlineButton(
onPressed: _logoutWithFB,
child: Text('Logout'),
),
],
)
: OutlineButton(
onPressed: _loginWithFB,
child: Text('Facebook login'),
color: Colors.blueAccent,
),
),
);
}
}
The logic I want to use is for sign in, the user sign up with facebook or google, I get some basic info and ask the user to add some further information in another screen, then on submission the user info and the token are sent to the backend (which is a node.js api).\
On the back I want to verify the token received from the front end with facebook or google and if the profile id match the one received the user info received from the front end is saved, then a JWT would be created and sent to the front end.
My challenge now is how do I verify the oauth token on the node.js side.

Answer 1

User -> SignIn Facebook -> Token generated -> Token Sent to Backend -> Middleware Nodejs -> check user_id exist -> generate JWT -> sendBackTo clientSide.
It's very simple you have to create a middleware function in your back-end nodejs in this case.
const express = require("express");
const app = express();
//function that return JWT token
String check_user_id(req,res,next) async
{
var uid = req.params.uid
//Query database check if userIdexist or not
check_db(uid)
//if it exist
next();
return GenerateJwt(userId)
else
{
//Signup the userid
SignUp(userId);
//generateJWT
next();
return GenerateJwt(userId);
}
}
app.get('/check_uid/:uid',check_user_id,(res,req,next) =>
{
res.send({'message':'verified'});
}