What is the best practice to use Oauth2, React, Node.js and Passport.js to authenticate user with Google sign on button?

Question

I want to have a login button in my website so when a user clicks on it, the user can use their Google credentials. I'd like to ideally perform the authentication server side using Express.js and Passport.js.

I implemented authentication server-side but the problem is that I can't make an AJAX request from the website to the server to start authentication because Google or Oauth don't support CORS. So I need to use a href element in my website which would call the server authentication endpoint. However, I can't catch server response in this way.

If I perform the authentication client-side (I'm using React) I could store login state in Redux and allow the user to access the website's resources. However, when the user logs out I need to make sure that server endpoints stop serving the same user which feels like implementing authentication twice: client-side and server-side.

In addition when authenticating client-side, Google opens a popup for the user to authenticate which I think is worse user experience then just a redirect when authenticating server-side.

I'm wondering what the best practice in terms of authenticating using Oauth2/Google. For example, stackoverflow.com also has Google button but just makes a redirect, without any popup, so I guess they figured out a way to perform server-side authentication and to bypass CORS issue.

Answer 1

Your authentication should be done server side. Here is how it works.

1. You make a fetch or axios call to your authentication route.
2. Your authentication route sends a request to Google's Authentication servers. This is important to have on the backend because you will need to provide your clientSecret. If you were to store this on the frontend, it would make it really easy for someone to find that value and compromise your website.
3. Google authenticates the user and then sends you a set of tokens to your callback url to use for that user (refresh, auth, etc...). Then you would use the auth token for any additional authorization until it expires.
4. Once that expires, you would use the refresh token to get a new authorization token for that client. That is a whole other process though.

Here is an example of what that looks like with Passport.js: https://github.com/jaredhanson/passport-google-oauth2

EDIT #1:

Here is an example with comments of the process in use with Facebook, which is the same OAuth codebase: https://github.com/passport/express-4.x-facebook-example/blob/master/server.js

Answer 2

I faced the same issue. This article is Gold link

1.In auth route File I had following code

 const CLIENT_HOME_PAGE_URL = "http://localhost:3000";

  // GET  /auth/google
  // called to authenticate using Google-oauth2.0
  router.get('/google', passport.authenticate('google',{scope : ['email','profile']}));


  // GET  /auth/google/callback
  // Callback route (same as from google console)
   router.get(
    '/google/callback',  
    passport.authenticate("google", {
    successRedirect: CLIENT_HOME_PAGE_URL,
    failureRedirect: "/auth/login/failed"
   })); 

   // GET  /auth/google/callback
  // Rest Point for React to call for user object From google APi
   router.get('/login/success', (req,res)=>{
     if (req.user) {
         res.json({
          message : "User Authenticated",
         user : req.user
        })
     }
     else res.status(400).json({
       message : "User Not Authenticated",
      user : null
    })
  });

2.On React Side After when user click on button which call the above /auth/google api

  loginWithGoogle = (ev) => {
    ev.preventDefault();
    window.open("http://localhost:5000/auth/google", "_self");
  }

3.This will redirect to Google authentication screen and redirect to /auth/google/callback which again redirect to react app home page CLIENT_HOME_PAGE_URL

4.On home page call rest end point for user object

(async () => {
  const request = await fetch("http://localhost:5000/auth/login/success", {
   method: "GET",
   credentials: "include",
   headers: {
    Accept: "application/json",
     "Content-Type": "application/json",
    "Access-Control-Allow-Credentials": true,
  },
});

const res = await request.json();
   //In my case I stored user object in redux store
   if(request.status == 200){
     //Set User in Store
    store.dispatch({
      type: LOGIN_USER,
      payload : {
        user : res.user
     }
    });
  }

})();

5.last thing add cors package and following code in server.js/index.js in node module

// Cors
app.use(
  cors({
    origin: "http://localhost:3000", // allow to server to accept request from different origin
    methods: "GET,HEAD,PUT,PATCH,POST,DELETE",
    credentials: true // allow session cookie from browser to pass through
   })
);