It's a generic "SSL configuration" - hardly differs from configuring HTTPS on a web server.
The OS will give you CA and CAPath defaults, so they only exist if you really need to override them.
Cipher is your own choice ... And there are a lot of wrong choices, but the preferrable ones change over time, so no definitive answer.
Key and Cert are just things that you have, but I've seen nginx reject them simply because of trailing spaces at EOF and stuff like that, so it's not like you can't go wrong there ...
Unfortunately, it's a little too nuanced to be covered by a CI-specific manual. If you already understand SSL/TLS you'll know what to do, and if you don't - you'll screw it up even with all the info available in front of you.
