using System;
using System.Web;
public class CustomHttpModule:IHttpModule 
{
public void Dispose() 
{
}
public void Init(System.Web.HttpApplication Appl) 
{
Appl.BeginRequest += new System.EventHandler(OnBeginRequest);
}
public void OnBeginRequest(object sender, EventArgs e)
{
HttpApplication app = (HttpApplication)sender;
app.Context.Response.Write("HttpModule says Hello!");
}
}

in web.config file

<httpModules>

<add type="CustomHttpModule.Test" name="CustomHttpModule">

</httpModules>

Answer:
 

Again a simple .NET Interview question Writing a HttpModule is a two step process.

Create a class which implements IhttpModule. 

    public class clsHttpModule : IHttpModule
    {

    public void Init(HttpApplication context)
    {
       this.httpApp = context;
       httpApp.Context.Response.Clear();
       httpApp.AuthenticateRequest += new EventHandler(OnAuthentication);
       httpApp.AuthorizeRequest += new EventHandler(OnAuthorization);
    ....
    ....
    ....
   
    }
    void OnAuthorization(object sender, EventArgs a)
    {
        //Implementation
    }
    void OnAuthentication(object sender, EventArgs a)
    {       
        //Implementation
    }    
    }

 Make a entry in the web.config file.

   <httpModules>
   <add name="clsHttpModule" type="clsHttpModule"/>
   </httpModules>

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