Shibboleth Developers

can someone point me toward a description of how to configure Tomcat 
to use a JAAS-based Realm, with JAAS using either ldap or 
kerberos.... (preferably ldap)

the tomcat doc available at

http://tomcat.apache.org/tomcat-5.5-doc/printer/realm-howto.html

states, as step 1, "Write your own LoginModule, User and Role classes 
based on JAAS "

I'm assuming someone somewhere has already done this...

... but, so far, google hasn't found anything useful

thanks!