public function putItem($cache, $key, $item)
    {
        $cache = self::encodeCache($cache);
        $key = self::encodeKey($key);
        $itm = new IronCache_Item($item);
        $req = $itm->asArray();
        $url = "projects/{$this->project_id}/caches/$cache/items/$key";

        $this->setJsonHeaders();
        $res = $this->apiCall(self::PUT, $url, $req);
        return self::json_decode($res);
    }