protected function expiration($key)
	{
		$lifetime = ini_get("session.gc_maxlifetime");

		$expire = $this->engine->get($key . '_expire');

		// Set prune period
		if ($expire + $lifetime < time())
		{
			$this->engine->delete($key);
			$this->engine->delete($key . '_expire');
		}
		else
		{
			$this->engine->replace($key . '_expire', time());
		}
	}