Advice for auth systems?

Hi!

I did some research to find ready authentication systems, but many of these have broken links or are dated (and I don't know if there are better solution for security purposes, I'm new in CI).

So I try to ask you if you can tell me some ready systems that have these features:
- Security
- Sign up / Login (if possible, with js/jquery to do ajax check for forms)
- Secure remember me (encrypt cookies with browser / last request and others like that, or in any case some secure approach to make it safe)
- Session and user data on mysqli

And, if possible, also:
- Access level management
- Back-end management

Things like ajax will be good for me not only to have fast result, but because with a ready example (by secure source) I also can learn how-to implement also ajax requests with CI in a good way...

Thank you!