`Samyoul\U2F\U2FServer\U2FServer::createChallenge()` always throws an exception in PHP 7.4. ``` Samyoul\U2F\U2FServer\U2FException: Unable to obtain a good source of randomness ``` [`openssl_random_pseudo_bytes`](https://www.php.net/manual/en/function.openssl-random-pseudo-bytes.php) has changed in PHP 7.4. See RFC: https://wiki.php.net/rfc/improve-openssl-random-pseudo-bytes