/**
  * Process IPN request from ClickBank. Only process POST request
  * 
  * @param	object	$_POST
  * @return	int		HTTP code 
  */
 public function ipn(SS_HTTPRequest $request)
 {
     if ($request->isPost()) {
         if (ClickBankManager::validate_ipn_request($request->postVars())) {
             ClickBankManager::process_ipn_request($request->postVars());
             return Director::get_status_code();
         }
     }
     return ErrorPage::response_for(404);
 }