Sending mail with Gmail (XOAuth2) and Nodemailer

my-mailer.js

'use strict';

var xoauth2 = require('xoauth2');
var nodemailer = require('nodemailer');
var smtp = require('nodemailer-smtp-transport');
var htmlToText = require('nodemailer-html-to-text').htmlToText;

// Sending mail with Gmail using XOAuth2
// http://masashi-k.blogspot.com.br/2013/06/sending-mail-with-gmail-using-xoauth2.html

/**
 * @param {Object} constants expects the following:
 * {
 *      stmp_host: 'smtp-relay.gmail.com',
 *      user: 'some@gmail.com',
 *      user_name: 'Some Name',
 *      clientId: '...........', // see link above how to get one
 *      clientSecret: '.......',
 *      refreshToken: '.......'
 * }
 */
function myMailer(constants) {
  this.token = '';
  this.xoauth2_generator = '';
  this.transporter = '';
  this.constants = constants;
}

myMailer.prototype.createTransporter = function() {
  var self = this;
  var constants = this.constants;
  
  return new Promise(function(resolve, reject) {
    self.createXOAuth().then(function() {
      self.transporter = nodemailer.createTransport(smtp({
        name: constants.stmp_host,
        host: constants.stmp_host,
        port: 587,
        secure: false,
        ignoreTLS: false,
        tls: { rejectUnauthorized: true },
        debug: false,
        auth: { xoauth2: self.xoauth2_generator }
      }));
      self.transporter.use('compile', htmlToText());
      resolve();
    })
    .catch((err) => reject(err));
  });
};

myMailer.prototype.getAccessToken = function(transporter) {
  var self = this;
  return new Promise(function(resolve, reject) {
    self.xoauth2_generator.getToken(function(err, token){
      if(err) reject(err);
      else {
        self.token = token;
        resolve();
      }
    });
  });
};

myMailer.prototype.createXOAuth = function() {
  var self = this;
  var constants = this.constants;
  return new Promise(function(resolve, reject) {
    self.xoauth2_generator = xoauth2.createXOAuth2Generator({
      user: constants.user,
      clientId: constants.clientId,
      clientSecret: constants.clientSecret,
      refreshToken: constants.refreshToken,
      accessToken: self.google_token
    });
    self.xoauth2_generator.getToken(function(err, token){
      if(err) reject(err);
      else {
        self.google_token = token;
        resolve();
      }
    });
  });
};

/**
 * @param {Object} data expects the following:
 * {
 *      subject: 'Hi There!',
 *      html: 'some<br>formatted<strong>text</strong>',
 *      to_name: 'Some Name',
 *      to_email: 'to_email@mail.com'
 * }
 */
myMailer.prototype.getMailObject = function(data) {
  var mail = {
    headers: {
      'X-Sender': this.constants.user_name + '<'+this.constants.user+'>'
    },
    from: this.constants.user_name + '<'+this.constants.user+'>'
  };
  
  return new Promise(function(resolve, reject) {
    mail.subject = data.subject;
    mail.html = data.html;
    mail.to = {
      name: data.to_name, 
      address: data.to_email
    };
    resolve(mail);
  });
};

myMailer.prototype.sendMail = function(mail) {
  var self = this;
  return new Promise(function(resolve, reject) {
    self.getAccessToken(self.transporter).then(function(){
      self.transporter.sendMail(mail, function(error, info) {
        if (error) {
          reject(error);
        } else {
          resolve(info);
        }
      });
    }).catch((err) => reject(err));
  });
};

module.exports = myMailer;

// USAGE
// testing-mailer.js

// response is coming (in my case) from REDIS
var constants = {
  stmp_host: 'smtp-relay.gmail.com',
  user: resp.SUPORTE_MAIL,
  user_name: resp.SUPORTE_NAME,
  clientId: resp.OAUTH_CLIENT_ID,
  clientSecret: resp.OAUTH_CLIENT_SECRET,
  refreshToken: resp.OAUTH_REFRESH_TOKEN
};

var Mailer = require('./my-mailer.js');
var mailer = new Mailer(constants);

mailer.createTransporter().then(function(){
  var send_info = {
    subject: 'A test!',
    html: 'some<br>formatted <strong>text</strong>',
    to_name: 'Some Name',
    to_email: 'some@gmail.com'
  };
  return mailer.getMailObject(send_info);
}).then(function(mail_obj){
  mailer.sendMail(mail_obj).then(function(info) {
    console.info('sent to: ', info);
    process.exit();
  }).catch(function(err) {
    console.info('error: ', err);
  });
});

This doesn't work, it complains about missing credentials for "PLAIN"

This doesn't work, it complains about missing credentials for "PLAIN"

I am getting the same error, how did you fix yours?