What is the use of HTTP modules ?

Answer:

HTTP modules are used to implement various application features, such as forms authentication, caching, session state, and client script services.
HTTP modules are executed before and after the handler and are used to provide a method for interacting with the request.
HTTP modules will let you know and examine the incoming requests and take action based on the request.They are also used to let you know and examine the outgoing response and modify it.