code: function vhost(hostname, router) {
    return function (req, res, next) {
      if (req.hostname === hostname) {
        router(req, res, next);
      } else {
        next();
      }
    };
  }
docs: Virtual hosts
  
  Express depends on vhost, so we don't have to.
  
  @param {string} hostname
  @param {express.Router} router
  @returns {Function}
  @see https://www.npmjs.com/package/vhost