Passport strategy for authenticating with Google using OAuth 2.0.

This module lets you authenticate using Google in your Node.js applications. By plugging into Passport, Sign In with Google can be easily and unobtrusively integrated into any application or framework that supports Connect-style middleware, including Express.

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$ npm install passport-google-oauth20

$ npm install @types/passport-google-oauth20

The Google strategy authenticates users using their Google account. Before your application can make use of Google's authentication system, you must first register your app to use OAuth 2.0 with Google APIs. Once registered, a client ID and secret will be issued which are used by Google to identify your app.

Once you've registered your application, the strategy needs to be configured with your application's client ID and secret, along with its OAuth 2.0 redirect endpoint.

The strategy takes a verify function as an argument, which accepts accessToken, refreshToken, and profile as arguments. accessToken and refreshToken are used for API access, and are not needed for authentication. profile contains the user's profile information stored in their Google account. When authenticating a user, this strategy uses the OAuth 2.0 protocol to obtain this information via a sequence of redirects and API requests to Google.

The verify function is responsible for determining the user to which the Google account belongs. In cases where the account is logging in for the first time, a new user record is typically created automatically. On subsequent logins, the existing user record will be found via its relation to the Google account.

Because the verify function is supplied by the application, the app is free to use any database of its choosing. The example below illustrates usage of a SQL database.

var GoogleStrategy = require('passport-google-oauth20');

passport.use(new GoogleStrategy({
    clientID: GOOGLE_CLIENT_ID,
    clientSecret: GOOGLE_CLIENT_SECRET,
    callbackURL: 'https://www.example.com/oauth2/redirect/google',
    scope: [ 'profile' ],
    state: true
  },
  function verify(accessToken, refreshToken, profile, cb) {
    db.get('SELECT * FROM federated_credentials WHERE provider = ? AND subject = ?', [
      'https://accounts.google.com',
      profile.id
    ], function(err, cred) {
      if (err) { return cb(err); }
      
      if (!cred) {
        // The account at Google has not logged in to this app before.  Create a
        // new user record and associate it with the Google account.
        db.run('INSERT INTO users (name) VALUES (?)', [
          profile.displayName
        ], function(err) {
          if (err) { return cb(err); }

          var id = this.lastID;
          db.run('INSERT INTO federated_credentials (user_id, provider, subject) VALUES (?, ?, ?)', [
            id,
            'https://accounts.google.com',
            profile.id
          ], function(err) {
            if (err) { return cb(err); }
            var user = {
              id: id,
              name: profile.displayName
            };
            return cb(null, user);
          });
        });
      } else {
        // The account at Google has previously logged in to the app.  Get the
        // user record associated with the Google account and log the user in.
        db.get('SELECT * FROM users WHERE id = ?', [ cred.user_id ], function(err, row) {
          if (err) { return cb(err); }
          if (!row) { return cb(null, false); }
          return cb(null, row);
        });
      }
    });
  }
));

Two routes are needed in order to allow users to log in with their Google account. The first route redirects the user to the Google, where they will authenticate:

app.get('/login/google', passport.authenticate('google'));

The second route processes the authentication response and logs the user in, after Google redirects the user back to the app:

app.get('/oauth2/redirect/google',
  passport.authenticate('google', { failureRedirect: '/login', failureMessage: true }),
  function(req, res) {
    res.redirect('/');
  });

• Using OAuth 2.0 to Access Google APIs

  Official Google documentation on how to use OAuth 2.0 to access Google APIs.

• todos-express-google-oauth2

  Illustrates how to use the Google strategy within an Express application.

• Jared Hanson { }

The MIT License

Copyright (c) 2012-2022 Jared Hanson <https://www.jaredhanson.me/>