function buildSignedParametersForApp($params)
{
$params = $this->prepareParameters($params);
$params['sign'] = urlencode($this->signParameters($params));
$params['sign_type'] = 'RSA';
$paramStr = [];
foreach ($params as $k => &$param) {
$param = '"' . $param . '"';
$paramStr[] = $k . '=' . $param;
}
return implode('&', $paramStr);
}