Reading OAM Http header variables through CGI script

I was working on providing single sign-on for one of the CGI applications. I had set header variables in Authorization Rule Actions for User ID and other attributes as say AUTH_USER etc., While trying to read the headers in CGI app with name AUTH_USER, it is not available.

Upon reading/displaying all the headers in CGI application, it was reading with HTTP_AUTH_USER instead of AUTH_USER. I'm wondering if this is the default behavior of CGI app for reading headers! You can post your thoughts too...