/**
  * Set the request protocol (https / http).
  * 
  * @param string $protocol
  * @throws Exception
  * @return Customweb_Core_Http_Request
  */
 public function setProtocol($protocol)
 {
     if ($protocol != 'http' && $protocol != 'https') {
         throw new Exception("You can either use HTTP or HTTPS in the URL. Other protocols are not supported.");
     }
     $this->url->setScheme($protocol);
     return $this;
 }