Get LTPA token once logged on

I heard you can get an LTPA token once I logged on to a Domino server. I use a combination of Tomcat servlets & Domino. I only want to use the LTPA token to create a new session under the logged-on user in Domino through a servlet. How can I get this token again. I use Singel Signon in Domino, and the user always first has to authenticate a first time in Domino