Loggin in via JBoss to several db accounts?

[Bjorn Stove]

Hi!
Im a newbie to JBoss. I have a web app that uses SQLServer.
Is it possible to have a log in in the app (j_security_check)
and letting that log in represent a db log in.
What I want is to give a user a separate db account already when he
logs in. So I can give different users different privileges in the db
already from start. As now I log in the db from xml file with only one
account for everybody.
Thankfull for advice.
Best Regards
Bjorn