The machine that runs the Proxy Module & authProxy must be marked as
trusted for delegation by the Active Directory domain
controller.  This is necessary for the proxy to automatically "pass
along" the users' authentication to the searched web sites.
Start -
  Programs - Administrative Tools -
  Active Directory Users and Computers.Computers on the left.Properties.Trust computer for delegation.  A message box
  warning you that "this is a security-sensitive operation and it
  should not be done indiscriminately" will pop up.  Click OK.OK to close the machine's properties, and close the
  Active Directory Users and Computers window.