The Power Of .Net Http Modules And Handlers (IHttpModule, IHttpHandler)
You can build your own application firewall
Stateful Web Application Firewalls with .NET
http://www.awprofessional.com/articles/article.asp?p=694855&f1=rss&rl=1
or even reverse proxy
Simple HTTP Reverse Proxy with ASP.NET and IIS
http://www.codeproject.com/aspnet/HTTPReverseProxy.asp
Cheers