It depends what you’re trying to achieve by using TLS. If you just want to authenticate with a client certificate while obscuring data from passive observers, then just a :certfile option may work, assuming this one file contains the client certificate, any intermediate certificates needed, and the private key. If the private key is stored in a separate file you’d have to pass a :keyfile option as well.
If you want to strongly authenticate the server, to prevent active (MitM) attacks, you’re going to have to pass in a few more options, starting with verify: :verify_peer, the server’s hostname (using the :server_name_indication option is easiest) and the trusted CA certificates (using the :cacertfile option, which may interfere with selection of the client certificate’s intermediate CA certs).
