Thursday, July 01, 2010

Config-free IHttpModule Registration

by via Nikhil Kothari's Weblog on 7/1/2010 2:29:57 PM

The ASP.NET pipeline allows HTTP modules to plug in into the request processing lifecycle and do work at various stages. For example, output caching, authentication, authorization etc. are all implemented as HTTP modules.

However one of the problems is that HTTP modules must be registered in configuration. This is a little painful for writing framework components where an HTTP module is essentially an implementation detail. You don't want every app developer using your framework to have to add in some configuration entries. What you want is the ability to programmatically add HTTP modules to the pipeline. This isn't available out-of-the-box today.

I faced this problem in my previous post around RIA Services, Authentication and Roles, as I needed to handle the PostAuthenticateRequest event. This seems to have come up before (for example here and here on stack overflow).

So in the interim, we can use the new, and somewhat obscure, ASP.NET 4.0 feature, the PreApplicationStartMethodAttribute, that lets you declare some code you want to run early in the initialization phase of your web application, even before any dynamic compilation happens and before any application startup code runs. Combine that capability with an HttpApplication that supports registering HTTP modules programmatically, as we're in business. I wrote DynamicHttpApplication that provides this API (link to code below):

public abstract class DynamicHttpApplication : HttpApplication {
    public static void RegisterModule(Func<HttpApplication, IHttpModule> moduleFactory);
}