code: protected function handlePostMessage($messageName, $lastResponse, $messageOptions, $result)
      {
          //CHECK FOR SESSION DATA:
          if ($this->isStateful() === true) {
              //We need to extract session info
              $this->sessionData = $this->getSessionDataFromHeader($lastResponse);
              $this->isAuthenticated = (!empty($this->sessionData['sessionId']) &&
                  !empty($this->sessionData['sequenceNumber']) &&
                  !empty($this->sessionData['securityToken']));
          } else {
              $this->isAuthenticated = false;
          }
      }
docs: Handles post message actions
  
  - look for session info and set status variables
  - checks for message errors?
  - ends terminated sessions
  
  @param string $messageName
  @param string $lastResponse
  @param array $messageOptions
  @param mixed $result
  @return void