authentication - admin only

[eluser]Mutsop[/eluser]
Hi,

I'm looking for a CI authentication "addon".
What I actually need is:

Admin only -> so no users nor registrations
admin can create other administrators and set permissions

thats it

I've been looking at some of auth addons in the wiki,
but most of them need to be modified alot.

Any ideas what other I might try?

Kindly regards