A document describing the NASA implementation of the authentication gateway.
A white paper describing how the University of Alberta created an authentication gateway.
Nocat.net has an authentication gateway for wireless networks. This software has a web based client.
Horatio: Authenticated Network Access is a firewall authentication tool. The premise: Legitimate users want to attach laptops and other mobile hosts to the network, but security demands that illegitimate users be prevented from accessing the internal, secure network and from abusing the general Internet.