Auth-User

Hi,
  With several of our web applications, when a user is authenticated, the
webserver sets the 'Auth-User' HTTP header to the name of the authenticated
user.
 
  Can anyone tell me if Auth-User originates in a w3c specification or some
other standard?  I've checked the HTTP RFCs, but haven't found any
reference.  I find Apache, iPlanet, and IIS all set this header so I imagine
it is defined in a spec or simply a de facto standard.
 
  I'm working with some Web Single Sign On software that sets another HTTP
header, not auth-user, which is causing problems for a lot of web
applications.  I suspect this isn't compliant to some standard but want to
be sure before I discuss with the vendor.
 
Chris Constantino
Programmer Analyst
U.S. Army Tank-automotive & Armaments Command
Warren, MI