code: function sanitize(sender, data) {
    data = _.defaults({}, {
      client_id: sender.client_id, client_secret: sender.client_secret
    }, data);
  
    return _.reduce(data, function (acc, value, key) {
      if (! _.isUndefined(value)) {
        acc[key] = value;
      }
      return acc;
    }, {});
  }
docs: merge send data with authorization data,
  remove all undefined values