Proper authentication method for a server application that runs as my own Twitch account?

Nope

Pretty much

That would be easiest.

You’d only have to authenticate once, and then make sure to refresh the token when it expires as per normal oAuth work flows.

Twitch offers a few options, but plain normal oAuth is the easiest.

What did you go for in the end, so others who find this thread have an answer?