1. HttpContext.Current.Request, Response

2.HttpHandler-> ProcessRequest

3.HttpModule-> Init, InitHandlers, context_BeginRequest

Comments:

This seems to be an event and handler based system. Can follow the design lines.

Kinds of DDD, HttpContext, naturally, there should be different Contexts, so, something can be infered from these code. Current? Request and Response, they are the basic lines of this Domain driven.

Maybe we can realize DDD and CQRS, CQRS  is like an architectural pattern, while DDD is used to handle different domain business, DDD varies with different domain.

A software should be an architecture and some OOP models(DOMAIN MODELs), no need to bother so much to know how it is realized, just watch out for you business. We have different styles.