Pass the AUTH USER to another application

Hello,

We have TOMCAT 5.5 running behind an IIS6 server.
We are using JAAS to authenticate the users on our internal developed JSP
based web site.
In order to achived the authentication - we must remove the "Use Integrated
Windows Authentication" checkbox on the IIS6 since otherwise the
authentication process is being done by IIS while our application is not
aware of the user just sign in.

Is this posible to get the AUTH USER parameter to be passed to our JSP pages.
Meaning the Authentication process it self will be done by IIS and the IIS
will pass the authenticated user as a parameter to our JSP pages?

Any other solution (except the migration to ASP based web site) will be
welcome.

Thank you for your help.
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"It will only take 5 minutes is not exiting in the IT world"