in signature/php/src/SignatureUtil.php [123:132]
public static function SHA256withRSASign($stringToSign, $secret)
{
if (!isset($stringToSign) || !isset($secret)) {
throw new \InvalidArgumentException('not a valid value for parameter');
}
$ret = '';
$privateKey = "-----BEGIN RSA PRIVATE KEY-----\n" . $secret . "\n-----END RSA PRIVATE KEY-----";
@openssl_sign($stringToSign, $ret, $privateKey, OPENSSL_ALGO_SHA256);
return Utils::toBytes($ret);
}