code: function getBearerToken(consumerKey, consumerSecret, callback) {
    const base64EncodedKey = new Buffer(`${consumerKey}:${consumerSecret}`).toString('base64')
    http
      .post('https://api.twitter.com/oauth2/token?grant_type=client_credentials')
      .set('Content-Type', 'application/x-www-form-urlencoded;charset=UTF-8')
      .set('Authorization', `Basic ${base64EncodedKey}`)
      .end(callback)
  }
docs: Obtain Twitter bearer token used for application api calls. Base64 encodes
  consumer key and secret, then sends request to /oauth2/token endpoint.
  
  @param {String} consumerKey
  @param {String} consumerSecret
  @param {Function} callback