You can edit jboss-4.2.0.GA/server/default/conf/jboss-log4j.xml if you are using jboss 4.2 or jboss-4.0.5.GA/server/default/conf/log4j.xml
and change :
<root> <level value="DEBUG"/> <appender-ref ref="CONSOLE"/> <appender-ref ref="FILE"/> </root>
but that is a lot of debug.
cool thing is that you do not have to stop server to change logging level
On the icefaces side, use firefox + firebug. You can see what is being sent to the server, and the response (which can be stack traces which don't always show up in the standard logs)
Attach a debugger to jboss and put breakpoints in your authentication method.
If all else fails you can always download the source for seam and put breakpoints in the seam src.