Twitter 3 legged OAuth on AWS Lambda with NodeJS

twitter_oauth_user_context.js

const OAuth = require('oauth');
const Twit = require('twit');
const nconf = require('nconf');

// temp global var
var oAuthTokenSecret;

// load config file which contains twitter app tokens
nconf.file({ file: './config/twitter-share.json' }).env()

// request user OAuth
const oauth = new OAuth.OAuth(
  'https://api.twitter.com/oauth/request_token',
  'https://api.twitter.com/oauth/access_token',
  nconf.get('consumer_key'),
  nconf.get('consumer_secret'),
  '1.0',
  //API ENDPOINT URL FOR oauthResponse LAMBDA BELOW e.g.
  ' https://xxxxxxxx.execute-api.xx-xxxx.amazonaws.com/dev/twitter/oauthResponse',
  'HMAC-SHA1'
);

// request app OAuth
const createT = (oAuthAccessToken, oAuthAccessTokenSecret) => new Twit({
	  consumer_key: nconf.get('consumer_key'),
    consumer_secret: nconf.get('consumer_secret'),
    access_token: oAuthAccessToken,
    access_token_secret: oAuthAccessTokenSecret
});

module.exports.oauthGET = (event, context, callback) => {
  oauth.getOAuthRequestToken((err, OAuthToken, OAuthTokenSecret, results) => {

    oAuthTokenSecret = OAuthTokenSecret;

    let html = [
      '<a href="https://api.twitter.com/oauth/authenticate?oauth_token=',
      OAuthToken,
      '">',
      'Sign in with twitter</a>'
    ].join('');

    const response = {
      statusCode: 200,
      headers: {
        'Content-Type': 'text/html',
      },
      body: html
    };

    callback(null, response);

  });
}

module.exports.oauthResponse = (event, context, callback) => {
  console.log(event);
  oauth.getOAuthAccessToken(
    event.query.oauth_token,
    oAuthTokenSecret,
        event.query.oauth_verifier,
        (err, oAuthAccessToken, oAuthAccessTokenSecret, results) => {
          let T = createT(oAuthAccessToken, oAuthAccessTokenSecret);
          T.post('statuses/update', { status: 'testing 3 Legs auth' }, (err, data, response) => {
      });
    });
}