You can use Quickstart for node.js. The detail information is https://developers.google.com/gmail/api/quickstart/nodejs. Using a sample script from Quickstart, you can retrieve access token by OAuth2, and retrieve email and user profile.

Before it runs a sample of Quickstart, please confirm Prerequisites, Step 1 and Step 2.

You can use by changing listLabels(auth) as follows. The scope is https://www.googleapis.com/auth/gmail.readonly.

Script :

var gmail = google.gmail({
        auth: auth,
        version: 'v1'
});

gmail.users.getProfile({
    auth: auth,
    userId: 'me'
    }, function(err, res) {
    if (err) {
        console.log(err);
    } else {
        console.log(res);
    }
});

gmail.users.messages.get({
    'userId': 'me',
    'id': 'mail ID',
    'format': 'raw'
}, function (err, res) {
    console.log(new Buffer(res.raw, 'base64').toString())
});

• gmail.users.getProfile retrieves user profile.
• gmail.users.messages.get retrieves email.

If I misunderstand your question, I'm sorry.

Added :

Please change above to following script. Scope is https://www.googleapis.com/auth/userinfo.profile.

Script :

var oauth2 = google.oauth2({
        auth: auth,
        version: 'v2'
});

oauth2.userinfo.v2.me.get(
function(err, res) {
    if (err) {
        console.log(err);
    } else {
        console.log(res);
    }
});

Result :

{
  id: '#####',
  name: '#####',
  given_name: '#####',
  family_name: '#####',
  link: '#####',
  picture: '#####',
  gender: '#####',
  locale: '#####'
}

You can also look into PassportJS. They have multiple strategies, including OAuth2 and 3 different Google Auth strategies. My answer doesn't really answer your question but maybe even taking a peek at Passport's code, you may get your answer.

http://passportjs.org/

2021 Solution

This answer may divert from the originally asked question but I think it will be useful for some people who are getting google user information in the backend by generating AuthUrl and sending it to the client side and then receiving the data response in the call back URL after the user gives permission from the client side.

Some global declarations

import { google } from "googleapis";
const Oauth2Client = new google.auth.OAuth2(
  googleCredentials.CLIENT_ID,
  googleCredentials.CLIENT_SECRET,
  googleCredentials.REDIRECT_URI
);

Generate the Auth URL with the scopes

const SCOPE = [
  'https://www.googleapis.com/auth/userinfo.profile', // get user info
  'https://www.googleapis.com/auth/userinfo.email',   // get user email ID and if its verified or not
];
const auth_url = Oauth2Client.generateAuthUrl({
  access_type: "offline",
  scope: SCOPE,
  prompt: "consent",
  state: "GOOGLE_LOGIN",
});
return res.json({ url: auth_url });    // send the Auth URL to the front end

Get the user data in the callback

let code = req.query.code;    // get the code from req, need to get access_token for the user 
let { tokens } = await Oauth2Client.getToken(code);    // get tokens
let oauth2Client = new google.auth.OAuth2();    // create new auth client
oauth2Client.setCredentials({access_token: tokens.access_token});    // use the new auth client with the access_token
let oauth2 = google.oauth2({
  auth: oauth2Client,
  version: 'v2'
});
let { data } = await oauth2.userinfo.get();    // get user info
console.log(data);    // you will find name, email, picture etc. here

Feel free to discuss in the comments if there's any confusion or error