passport.js

const GoogleStrategy = require('passport-google-oauth20').Strategy
const mongoose = require('mongoose')
const User = require('./models/User.js')
// Creating the Google Strategy for the passport middleware
module.exports = function(passport) {
    passport.use(new GoogleStrategy({
        clientID: process.env.CLIENT_ID,
        clientSecret: process.env.CLIENT_SECRET,
        callbackURL: '/auth/google/callback'
    }, async (accessToken, refreshToken, profile, done) => {
        const newUser = {
            googleId: profile.id,
            displayName: profile.displayName,
            firstName: profile.name.givenName,
            lastName: profile.name.familyName,
            image: profile.photos[0].value
        }

        try {
            let user = await User.findOne({ googleId: profile.id })

            if (user) {
                done(null, user)
            } else {
                user = await User.create(newUser)
                done(null, user)
            }
        } catch (error) {
            console.error(error)
        }
    }))
    // Serialising and deserialising the user for subsequent requests
    passport.serializeUser((user, done) => {
        done(null, user.id)
    })
    passport.deserializeUser((id, done) => {
        User.findById(id, (err, user) => done(err, user))
    })
}