tls_identity(
cert_path,key_path,hostname) ->identity,err
Parse a cert+key PEM pair into a reusable TLS identity
Parses the PEM certificate chain and private key from files into
a Lua userdata that can be passed to starttls() via the identity
config field. The identity is parsed once and reused across connections,
avoiding per-connection file I/O and PEM parsing overhead.
The optional hostname is stored for SNI matching.