code: function(field){
              var req = this.req;
              field = field.toLowerCase();
              switch (field) {
                  case 'referer':
                  case 'referrer':
                  return req.headers.referrer || req.headers.referer || '';
                  default:
                  return req.headers[field] || '';
              }
          }
docs: Return request header.
  
  The `Referrer` header field is special-cased,
  both `Referrer` and `Referer` are interchangeable.
  
  Examples:
  
  this.get('Content-Type');
  // => "text/plain"
  
  this.get('content-type');
  // => "text/plain"
  
  this.get('Something');
  // => undefined
  
  @param {String} field
  @return {String}
  @api public