function buildSignedParameters($params)
{
$params = $this->prepareParameters($params);
$params['sign'] = $this->signParameters($params);
if ($params['service'] != self::SERVICE_WAP && $params['service'] != self::SERVICE_WAP_AUTH) {
$params['sign_type'] = strtoupper(trim($this->config['sign_type']));
}
return $params;
}