Auth

I use Ion Auth, but only parts of it. Eventually I may do my own, but for now, Ion Auth works pretty well.

I don't believe Codeigniter needs an authentication module. There are plenty around, and it's quite easy to do your own (The advantage of doing your own is that you get something that fits perfectly with what you are trying to achieve, plus you get to learn more about Codeigniter and how to extend it yourself).