Hi guys,
Plain simple,which auth system would you recommend.I have the below requirements :

Maximum security(DoS Attacks and Brute Force Attacks included)
Simple configuration-implementation
Very well documentation.
Admin functionality
User roles.

Thanks in advance!

tank auth
http://konyukhov.com/soft/tank_auth/

There are a few you might try:

Community Auth
AG Auth
Ion Auth
Tank Auth
DX Auth

and probably more in the wiki.

Ion Auth 2 is good, https://github.com/benedmunds/CodeIgniter-Ion-Auth

But the lack of documentation kind of sucks. It does come with full working examples for creating users, forgot password, etc etc. My only complaint is the lack of documentation… but you CAN get by simply by looking at the source.