public function incrementItem($cache, $key, $amount = 1)
    {
        $cache = self::encodeCache($cache);
        $key = self::encodeKey($key);
        $url = "projects/{$this->project_id}/caches/$cache/items/$key/increment";
        $params = array(
            'amount' => $amount,
        );
        $this->setJsonHeaders();
        return self::json_decode($this->apiCall(self::POST, $url, $params));
    }