Hi Sam,
You probably want to look into hooking into the authentication events published by the framework, which uses the standard Spring ApplicationListener functionality. The Spr Sec framework ships with "LoggerListener", which should provide you with an example of how to use these. Refer to the Javadoc for the relevant classes
here.
Best,
Peter
Author, Spring Security 3 (the Book), Packt Publishing, 2010
SCJP, OCP