how to automatically get the authorization token for node google apis for gmail

Question

I'm having trouble figuring out how to get the authorization to be automatic for a user. I need to get the oauth token automatically becuase my software is all voice command, but when you try and retrieve a users email it gives you a like to go and authorize the app, how do I make my code automatically get the auth token and authorize the app?

I'm trying to do this node and angular so that a users emails will update in realtime like notifications on my desktop app. This is the example code google gives, but it looks for an input of that token. I need to know how to get that token automatically.

Am I just missing something here with the code:

(function() {
  'use strict';

  function EmailService($window, $http, $rootScope, $q) {

    var service = {};
    service.events = [];
    service.getEmail = function() {

    var fs = require('fs');
    var readline = require('readline');
    var google = require('googleapis');
    var googleAuth = require('google-auth-library');


    // If modifying these scopes, delete your previously saved credentials
    // at ~/.credentials/gmail-nodejs-quickstart.json
    var SCOPES = ['https://www.googleapis.com/auth/gmail.readonly'];
    var TOKEN_DIR = '.credentials/';
    var TOKEN_PATH = TOKEN_DIR + 'gmail-nodejs-quickstart.json';

    // Load client secrets from a local file.
    fs.readFile('configs/client_secret.json', function processClientSecrets(err, content) {
      if (err) {
        console.log('Error loading client secret file: ' + err);
        return;
      }
      console.log(JSON.parse(content));
      authorize(JSON.parse(content), listLabels);
    });

    /**
     * Create an OAuth2 client with the given credentials, and then execute the
     * given callback function.
     *
     * @param {Object} credentials The authorization client credentials.
     * @param {function} callback The callback to call with the authorized client.
     */
    function authorize(credentials, callback) {
      var clientSecret = credentials.installed.client_secret;
      var clientId = credentials.installed.client_id;
      var redirectUrl = credentials.installed.redirect_uris[0];
      var auth = new googleAuth();
      var oauth2Client = new auth.OAuth2(clientId, clientSecret, redirectUrl);
      console.log(oauth2Client);

      // Check if we have previously stored a token.
      fs.readFile(TOKEN_PATH, function(err, token) {
        if (err) {
          getNewToken(oauth2Client, callback);
        } else {
          oauth2Client.credentials = JSON.parse(token);
          callback(oauth2Client);
        }
      });
    }

    /**
     * Get and store new token after prompting for user authorization, and then
     * execute the given callback with the authorized OAuth2 client.
     *
     * @param {google.auth.OAuth2} oauth2Client The OAuth2 client to get token for.
     * @param {getEventsCallback} callback The callback to call with the authorized
     *     client.
     */
    function getNewToken(oauth2Client, callback) {
      var authUrl = oauth2Client.generateAuthUrl({
        access_type: 'offline',
        scope: SCOPES
      });

      console.log('Authorize this app by visiting this url: ', authUrl);
      var rl = readline.createInterface({
        input: process.stdin,
        output: process.stdout
      });
      rl.question('Enter the code from that page here: ', function(code) {
        rl.close();
        oauth2Client.getToken(code, function(err, token) {
          if (err) {
            console.log('Error while trying to retrieve access token', err);
            return;
          }
          oauth2Client.credentials = token;
          storeToken(token);
          callback(oauth2Client);
        });
      });
    }

    /**
     * Store token to disk be used in later program executions.
     *
     * @param {Object} token The token to store to disk.
     */
    function storeToken(token) {
      try {
        fs.mkdirSync(TOKEN_DIR);
      } catch (err) {
        if (err.code != 'EEXIST') {
          throw err;
        }
      }
      fs.writeFile(TOKEN_PATH, JSON.stringify(token));
      console.log('Token stored to ' + TOKEN_PATH);
    }

    /**
     * Lists the labels in the user's account.
     *
     * @param {google.auth.OAuth2} auth An authorized OAuth2 client.
     */
    function listLabels(auth) {
      var gmail = google.gmail('v1');
      gmail.users.labels.list({
        auth: auth,
        userId: 'me',
      }, function(err, response) {
        if (err) {
          console.log('The API returned an error: ' + err);
          return;
        }
        var labels = response.labels;
        if (labels.length == 0) {
          console.log('No labels found.');
        } else {
          console.log('Labels:');
          for (var i = 0; i < labels.length; i++) {
            var label = labels[i];
            console.log('- %s', label.name);
          }
        }
      });
    }


};

return service 
}

angular.module('myApp')
    .factory('EmailService', EmailService);

}());