Forms Authentication and the Intranet Domain User

I have spent all day trying to find a way to get the domain user account of the client in a forms authentication environment.  I do not want to do windows authentication, because to much information is needed and gathered through the forms auth process.  I just need the username, then I query the AD to find the information that I need.  Does anyone have any ideas.  The key here is that I do not need to authenticate the user.  I would like to avoid a query string, since I am not authenticating based on the username a query string would be to insecure.  Any Ideas
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