var twitterConsumerKey = '';
var twitterConsumerSecret = '';

var OAuth2 = require('oauth').OAuth2;
var oauth2 = new OAuth2(
  twitterConsumerKey,
  twitterConsumerSecret,
  'https://api.twitter.com/',
  null,
  'oauth2/token',
  null
);
oauth2.getOAuthAccessToken(
  '',
  {'grant_type':'client_credentials'},
  function (e, access_token, refresh_token, results){
     console.log('bearer: ',access_token);
  }
);