how to Security Token transfer to J2EE web application?

Here is 2 web applications: 1 is asp.net, another is J2EE base webapplication.
Both them are using same AD ( e.g. DomainTest ) as authentication source.
Question here:
1. User log in the asp.net application ( form based log in DomainTest, not IE prompt authencation dialog ), on the left navigation ( link to J2EE web application), just click this link, SSO to J2EE application.
I think should transfer identity token from asp.net to J2EE, but don't know how, and for JSP, how to modify it to use token tranferd from asp.net ?
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