Session in Webapp

Dear Friends,
I've developed a Webapp for Jahia (or portlet) and I require one 
variable to be stored into HttpSession.

Since i do use the webapp outside jahia everything is fine, once i try 
it inside Jahia the session variable isn't keept.

Is there a configuration to change in order to share the session between 
jahia and webapp contexts ?

or

Basically i just need to carry around an ID (actually a user profile, 
but i can retrive via ID on each request)


thanks a lot for help!

-- 
Lorenzo Patocchi
Dipl. Ing. STS/ETS/HTL
www.cryms.com

Cryms sagl
Via Cantonale 34a
6928 Manno - Lugano
Switzerland