I have uploaded a new RADIUS Client library for ArduinoMega and the Arduino Ethernet shield. It implements a basic RADIUS Client, including packet creation, adding attributes, signing and encryption, sending and receiving requests, checking authenticators, getting attributes etc. Includes a UDPSocket class for managing UDP sockets. Tested against Radiator RADIUS Server (Radiator | Radiator Software)
Details at Radius: RADIUS Library for Arduino
Feedback to me: mikem@open.com.au
Cheers.