There are two ways in which you can inject logic in the request pipeline of an ASP.NET application — HttpHandlers and HttpModules. An HttpModule is a component that is part of the ASP.NET request ...
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.