How can I determine the number of users on an ASP.NET site (IIS)? And their info?

Is there a way to determine the number of users that have active sessions in an ASP.NET application? I have an admin/tools page in a particular application, and I would like to display info regarding all open sessions, such as the number of sessions, and perhaps the requesting machines’ addresses, or other credential information for each user.

Modifying headers with IIS7 Application Request Routing

I’m using IIS7 Application Request Routing in front of Tomcat as a replacement for ISAPI redirection. The basic reverse proxy function is working well, but I don’t have enough information in the final request headers. My application exists on several subdomains: customerone.ourservice.com, customertwo.ourservice.com, etc. Each subdomain runs the same application, but with different branding graphics.