RFE: seamlessly log in when necessary

[ktdreyer]

Instead of peppering the code with many ensure_logged_in() calls, we should update the central client code with a list of RPCs that require authentication, and then silently authenticate if we call an RPC on that list and we're not yet logged in.

Not sure how easily we can do this for multicalls. Research needed.

If this idea proves useful and robust, we might be able to submit this to Koji upstream. This would make it easier to use the client and to avoid unnecessary authentications.