What kind of authentication are you using?
I think the REMOTE_USER field you're referring to is a CGI variable--not an actual HTTP header. For basic auth, this is parsed from the Authorization header. The format for this header is:
Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==
Basic indicates the use of basic auth. The string after Basic is a base64 encoding of the username:password (Aladdin:open sesame, in this example).
You could use the HTTP::username command (
Click here) to return the parsed and decoded username.
For details on basic auth you can check this wikipedia article:
http://en.wikipedia.org/wiki/Basic_access_authentication
Aaron