OAuth 2.0 with Google API in Node.js

This blog post was originally posted on dev.to

With all the async awaits, promises, .then and all the other JS-specific stuff, doing even simple tasks in Javascript can feel overwhelming for beginner backend developers.

To preface, I'm currently working on my own application which is a simple Match betting tracker to keep track of my bets, and decided to add OAuth authentication in the app to let users log in from their Gmail account.

The first thing I did was set up an account in Google console, and got me some shiny new credentials (client ID and client Secret) for OAuth 2.0.

Understanding the authentication flow with all the tokens and secrets can seem daunting. So this quick guide will show you that it is quite simple, and help you get started with OAuth 2 authentication in your own app.

The first thing you need to do is get the Google API npm package:

  npm install googleapis

In the actual program:
Initialize the API library and set up google config.

const { google } = require('googleapis');
const oauth2 = google.oauth2('v2');

const Oauth2Client = new google.auth.OAuth2(
    process.env.GOOGLE_CLIENT_ID,
    process.env.GOOGLE_CLIENT_SECRET,
    process.env.GOOGLE_REDIRECT, // this must match your google api settings
);

So basically all you have to do are these three things:

1. get a Redirect url for the clients
2. The url also contains a code which then I use to get a token ( if the user signs in to their Google account that is)
3. And finally, I use the token to get the user details

Step 1:

function getConnectionUrl() {
    return Oauth2Client.generateAuthUrl({
        access_type: 'offline',
        prompt: 'consent',
        scope: defaultScope
    });
}

//Call this function somewhere in the program to get URL:
//const url = getConnectionUrl();

Step 2 and 3:

function getUserDetails(code) {
    return Oauth2Client.getToken(code)   //use code to get the token
        .then(({ tokens }) => {
            Oauth2Client.setCredentials(tokens);     //add token to the Oauth credentials
        })
        .then(() => {
            return oauth2.userinfo.get({ auth: Oauth2Client });  // get userinfo with the newly updated credentials
        })
}

UPDATE

Using async-await steps 2 and 3 can be reduced to::

 function async getUserDetails(code) {
   const {tokens} = await Oauth2Client.getToken(code);
   Oauth2Client.setCredentials(tokens);
   const usr_info = await oauth2.userinfo.get({auth: Oauth2Client});
   return usr_info;
 } 

This looks cleaner and async-await is a lot more intuitive to use.

And so in the main program , we get the connection URL using getConnectionUrl() which then gives you the code in the URL which I passed on to getUserDetails() to get the user details.

So this is how I got OAuth authentication working in my application.

Check out the full repo at:

• Matched-betting-tracker

Thanks for reading!