public function __construct()
 {
     // Successful Responses: A server receiving a valid request MUST send a
     // response with an HTTP status code of 200.
     parent::__construct(self::HttpOkResponse, self::IndirectResponseContentType);
     /*
      * This particular value MUST be present for the response to be a valid OpenID 2.0
      * response. Future versions of the specification may define different values in order
      * to allow message recipients to properly interpret the request.
      */
     $this[OpenIdProtocol::param(OpenIdProtocol::OpenIDProtocol_NS)] = OpenIdProtocol::OpenID2MessageType;
 }