Google\Spreadsheet\DefaultServiceRequest::post PHP Method

    public function post($url, $postData)
    {
        $headers = array("Content-Type: application/atom+xml", "Content-Length: " . strlen($postData));
        $ch = $this->initRequest($url, $headers);
        curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
        curl_setopt($ch, CURLOPT_POSTFIELDS, $postData);
        return $this->execute($ch);
    }