I have a filter (c/c++) on a site that handles authentication. A user
logs in using a username and password, the ISAPI filter looks up the
username in a database and then maps the username to another username
that is equal for all users (IUSR_SOMEUSER).

Later I need the individual username that the user has entered in the
first place. In asp I can get it from Servervariables("REMOTE_USER")
but in asp.net Servervariables("REMOTE_USER") contains the new
username. Why isn't the servervariables the same in .net??

If I log in with username mv I get

in asp:
REMOTE_USER = mv
AUTH_USER = IUSR_SOMEUSER

but in asp.net:
REMOTE_USER = COMPUTER\IUSR_SOMEUSER
AUTH_USER = IUSR_SOMEUSER