Google-api-nodejs-client: .getToken returning invalid_request

I am getting an error each time I call getToken with a valid authCode. Here is the error log printed via the code below:

Error getting tokens:  invalid_request

Is there something wrong with the way I am using the APIs? Appreciate any pointers...

var express = require('express');
var router = express.Router();
var google = require('googleapis');
var urlshortener = google.urlshortener('v1');
var OAuth2 = google.auth.OAuth2;
var plus = google.plus('v1');
var googleClientInfo = { "web": {...} };
var oauth2 = new OAuth2(googleClientInfo.web.client_id, googleClientInfo.web.client_secret, googleClientInfo.web.redirect_uris);
var scopes = [  'https://www.googleapis.com/auth/plus.me',
  'https://www.googleapis.com/auth/calendar'
];
google.options({ auth: oauth2 }); // set auth as a global default
var authUrl = oauth2.generateAuthUrl( {
  access_type: 'offline',
  scope: scopes
});

/* GET authCode from Google Server */
router.get('/', function(req, res) {
  console.log('Redirecting to URL: ' + JSON.stringify(authUrl));
  res.redirect(authUrl);
});

/* '/successful' is the redirect_uri with authCode query */
router.get('/successful', function(req, res) {
  console.log('Got code: ', (req.query.code));
  oauth2.getToken(req.query.code, function(err, tokens) {
    if(err) {
        console.log("Error getting tokens: ", err);
        res.redirect('/');
    } else {
        console.log("Saving tokens: ", JSON.stringify(tokens));
        // Save tokens
        oauth2.setCredentials(tokens);
        plus.people.get({ userId: 'me', auth: oauth2 }, function(err, response) {
          if(err) {
              console.log("Error getting userId: ", err);
              res.redirect('/');      
          } else {
              res.send('Login Successful: ' + JSON.stringify(response));
              console.log('Login Successful: ' + JSON.stringify(response));
          }
        });
    }
  });
});

module.exports = router;