Function common_name_matches 

fn common_name_matches(cert: &Certificate, server_name: &ServerName<'_>) -> bool

Returns whether server_name is a DNS name equal, ignoring ASCII case, to any subject common name of cert, and cert has no DNS or IP subjectAltName.

This is stricter than OpenSSL’s fallback, which also applies when only IP subjectAltNames are present, matches wildcard common names, and decodes string types other than UTF8String, PrintableString and IA5String.