Find out Who-I-Am for Realm User

Hi,

I am using realm for the authorization of my web application. I would like
to include a administration section for things like modifying the user
profile or password. I have several different user names associated with
two different roles. Both roles give the pass to the web pages. I am
wondering whether I can find out who is the login user in realm? So I do
not need the user to provide it again to entering the admin part. I am
using Tomcat 5.5 on a linux box. Thanks.

Sincerely
Zhu, Guojun