I want to let users to connect to my `node.js server` with their `gmail`. I have created a project in the `Google Developers Console`. Then use the following code:

```
const express = require('express');
const google = require('googleapis');
const googleAuth = require('google-auth-library');

const credentials = require('../link/of/some/file.json'); // google credential

let clientSecret = credentials.web.client_secret;
let clientId = credentials.web.client_id;
let redirectUrl = credentials.web.redirect_uris[0];

const SCOPES = [
   'https://mail.google.com/',
   'https://www.googleapis.com/auth/gmail.modify',
   'https://www.googleapis.com/auth/gmail.readonly'
];

let auth = new googleAuth();
let oauth2Client = new auth.OAuth2(clientId, clientSecret, redirectUrl);

app.get('/connect', (req, res) => {
   let authUrl = oauth2Client.generateAuthUrl({
      access_type: 'offline',
      scope: SCOPES
   });
   res.redirect(authUrl);
});

```

when `/connect` is called, it will redirect to google page to verify user. After user give access of his/her account, google will automatically call the following api with a `code` query parameter:

```
app.get('/auth/callback', (req, res) => {
    // 'req.query.code' is provided by google
    return oauth2Client.getToken(req.query.code, (err, token) => {
       // token value:
       /*
          { 
             access_token: 'ya29.Gls2Ba_rXEA5EoBaFH5bPdDDzgaSWOtb0GSJcnaTP47Jh7HwHdF2ZJZOlQaCJBC5wjpq-sOLBVlIM9L8BMslVyHw22nveU0MwQ4iJPTq5vkjXDeitqtoYH8JO83w',
             refresh_token: '1/S0C3w-8vnqcrGE4Z2mSW9ctYkaitVuZquBSJ0WJJHUs',
             token_type: 'Bearer',
             expiry_date: 1514897380473 
          }
       */
    });
});

```

Now, My problem is, in the above token value, I cannot understand how can I get gmail address from that token. What am I missing???

Any Suggestion? Thanks in advance.