public function TransientKey($NewKey = NULL) {
      if (!is_null($NewKey)) {
         $this->_TransientKey = Gdn::Authenticator()->GetUserModel()->SetTransientKey($this->UserID, $NewKey);
      }

//      if ($this->_TransientKey)
         return $this->_TransientKey;
//      else
//         return RandomString(12); // Postbacks will never be authenticated if transientkey is not defined.
   }