feature request: client certificates

[velartrill]

znc and services on many IRC networks support the use of certificates to authenticate the end user. this is superior to password authentication because each device can be provisioned with its own certificate that can be individually revoked and remains valid if the user changes his or her password. most prominent IRC clients, such as konversation and hexchat, support either TLS client certificates, SASL certificate auth, or both. however, no communi client offers a mechanism to accomplish this and a quick scan of the libcommuni source suggests it doesn't expose the necessary API to implement certificate support.