code: function headerFactory(key, value) {
    
    var headers = {};
    if (arguments.length === 2) {
      headers[key] = value;
    } else {
      headers = key;
    }
    return function header(req, res, next) {
      for (var name in headers) {
        if (headers.hasOwnProperty(name)) {
          res.setHeader(name, headers[name]);
        }
      }
      next();
    };
  }
docs: /* This Source Code Form is subject to the terms of the Mozilla Public
  License, v. 2.0. If a copy of the MPL was not distributed with this
  file, You can obtain one at http://mozilla.org/MPL/2.0/.