We currently have a situation where we need the ability to fully impersonate a login on a SharePoint Web Application. Effectively any "SuperUser" needs the ability to, without a password, proxy login as another user and see all that this user sees. Is there a way to accomplish this in SharePoint 2010?
Kerberos and NTLM will not allow this though it could be done via Forms authentication but you would have to write your own provider and install your own "back door" to enable this behavior. It could also possibly be done via Claims authentication.
However, doing something like this pretty much violates every security standard out there. I can understand the desire for such a feature but it utterly destroys any pretense of security and accountability. You are also in for no end of grief when your 'back door' is eventually leaked to the overall user community that you support.