<?php openssl_cms_sign( string $input_filename, string $output_filename, OpenSSLCertificate|string $certificate, OpenSSLAsymmetricKey|OpenSSLCertificate|array|string $private_key, ?array $headers, int $flags = 0, int $encoding = OPENSSL_ENCODING_SMIME, ?string $untrusted_certificates_filename = null): bool