In an earlier column I showed how to add custom processing to every request or response that your ASP.NET MVC or ASP.NET Web API site receives or produces. In that column, I offhandedly remarked about ...
When a request comes in to your ASP.NET site, it's routed through a series of message handlers (in ASP.NET Web API) or modules (in ASP.NET MVC), each of which performs some operation on the request.