apppool identity vs logged in user

I have a question about apppool identity and logged in user in asp.net. I have a UI running under an app pool identity. This UI communicates with a web service that handles authorization of the logged in user. The issue is that since the UI runs under an apppool identity, the web servicwe authorization tries to autorize the app poolidentity instead of the logged in user. I cannot use the HttpContext.Current.User.Identity since it is a web service and Current is nu开发者_Go百科ll. Is there a way to get the logged in user, other than passing its name as a parameter. Thanks for any help Laurent

Try searching for constrained delegation. Double-hop constrained delegation to be exact.

http://msdn.microsoft.com/en-us/library/ff649317.aspx