google-setup.js

const passport = require('passport');
const GoogleStrategy = require('passport-google-oauth20').Strategy;
require('dotenv').config({ silent: process.env.NODE_ENV === 'production' });
const User = require("./models/user");

passport.use(new GoogleStrategy({
    clientID: process.env.GOOGLE_CLIENT,
    clientSecret: process.env.GOOGLE_SECRET,
    callbackURL: process.env.BASE_URL + "/auth/google/redirect",
    userProfileURL: "https://www.googleapis.com/oauth2/v3/userinfo"
  },
async (token, tokenSecret, profile, done) => {
  // find current user in UserModel
  const currentUser = await User.findOne({
    _id: profile.id
  });
  // create new user if the database doesn't have this user
  if (!currentUser) {
    const newUser = await new User({
      _id: profile.id,
      displayName: profile.displayName
    }).save();
    if (newUser) {
      done(null, newUser);
    }
  }
  done(null, currentUser);
    }
  )
);