Best Auth library?

[eluser]jwright[/eluser]
It would be nice to see some auth framework directly incorporated into CI itself.
I don't know if this would or wouldn't go against what CI is all about. But what I'm interested in (and what I've seen with CI so far) is a framework where a bunch of stuff is included out of the box (the standard "don't reinvent the wheel" stuff) but most if not all that "stuff" is optional.

I think a basic auth/user/admin system would qualify as "don't reinvent the wheel" stuff.