Single Sign-on with Active Directory

I have a requirement in my project for SSO with Active Directory . Users should be allowed to login to their Windows desktop and not have to authenticate themselves to any web apps deployed under Tomcat.

I have been doing research on this for few days. We already use JOSSO in our project for Single sign-on. But from what i read about the integration of JOSSO with Active Directory i have understood that it does not support SPNEGO. So i need to enter my user name and password even though i have already logged into my Windows Desktop. So JOSSO is not a good solution to my problem.

I also read about few third party tools like centrify, Vintela and SPNEGO SSO. But none of them are opensource.
I would like to know if there are any open source tools available for this.

Thanks in advance,
Vidya