Description:
------------
---
From manual page: https://php.net/function.openssl-cms-sign
---

The documentation states the following:

> certificate
> The name of the file containing the signing certificate.
> 
> private_key
> The name of file containing the key associated with certificate.

This is incorrect and results in "PHP message: PHP Warning:  openssl_cms_sign(): Error getting private key in file.php". It actually has to be formatted per <https://www.php.net/manual/en/openssl.certparams.php>, so for example `file://cert.pem`.

Test script:
---------------
// Incorrect code (following documentation)
openssl_cms_sign('input.txt', 'output.txt', 'cert.pem', 'privkey.pem', null, OPENSSL_CMS_BINARY, OPENSSL_ENCODING_DER, 'chain.pem');

// Correct code
openssl_cms_sign('input.txt', 'output.txt', 'file://cert.pem', 'file://privkey.pem', null, OPENSSL_CMS_BINARY, OPENSSL_ENCODING_DER, 'chain.pem');