15.1. Using HttpModules

As we mentioned in chapter 1, HttpModules are a special kind of class used to intercept mainly HttpApplication events (but you can handle events from any object if you need to). An HttpModule implements the IHttpModule interface from the System.Web namespace and is loaded at runtime. Generally, HttpModules are stateless with regard to the current request, so they don’t contain state related to the current request, but they do use HttpContext (a singleton class) as their state context.

HttpContext offers access to both HttpRequest and HttpResponse, enabling state to be used across request and response. You also have the ability to use session state, caching, and application state.