If your application and IIS are setup for NTML authentication, then no, it's
not necessary.  The User.Identity.Name will return the Domain\username of
the user and you can use User.Identity.IsAuthenticate as a boolean to test
whether or not the user is authenticated.

If, from there, you need information from Active Directory (display name,
etc), the DirectoryServices namespace allows you to take that Identity.Name
and query up AD information (http://msdn2.microsoft.com/en-us/library/system.directoryservices.aspx).

From there, authentication is now taken care of and authorization is left
up to you and how you implement security in your application.

HTH.

-dl

--
David R. Longnecker
http://blog.tiredstudent.com