code: public function saveUrl($url = false, $append = '')
      {
          // If no URL is specified, then save the current URL.
          if ($url == false) {
              $url = '//'.$this->config['base_url'].$_SERVER['REQUEST_URI'];
          }
          
          // Set saved URL
          $this->saved = $this->getRedirect($url).$append;
          
          // Also save URL to session, in-case it won't be used until next request.
          $this->session->savedUrl = $this->saved;
      }
docs: For situations such as where a not-logged-in user tries to access a restricted page,
  you may want to save the URL they were trying to go to, so you can try forwarding them
  to it again after they login.