How can you modify or intercept incoming requests using an HttpModule?

To modify or intercept incoming requests using an HTTP module, you can leverage the event handlers available in the ASP.NET request processing pipeline. Here's an example of how you can achieve this:

1. Implement the 'IHttpModule' interface to create your custom HTTP module. This interface requires the implementation of the 'Init' and 'Dispose' methods.

   
   
   public class CustomModule : IHttpModule
   {
       public void Init(HttpApplication context)
       {
           // Subscribe to the desired event handlers
           context.BeginRequest += OnBeginRequest;
       }
   
       public void Dispose()
       {
           // Cleanup resources, if needed
       }
   
       private void OnBeginRequest(object sender, EventArgs e)
       {
           // Custom logic to modify or intercept the incoming request
           HttpContext context = ((HttpApplication)sender).Context;
   
           // Access and modify request details
           HttpRequest request = context.Request;
           // Modify request headers, query parameters, form data, etc.
   
           // Redirect the request
           // context.Response.Redirect("newpage.aspx");
   
           // Deny access to the request
           // context.Response.StatusCode = 403; // Forbidden status code
   
           // Perform custom request processing
           // ...
       }
   }
   
   

2. In the 'Init' method of your HTTP module, subscribe to the desired event handler(s). For example, you can subscribe to the 'BeginRequest' event to intercept requests as early as possible in the pipeline.
3. In the event handler(s), such as 'OnBeginRequest' in the example above, you can access the incoming request and modify it as needed. Here are some common modifications or interceptions you can perform:
   • Access and modify request headers, query parameters, form data, cookies, etc.
   • Redirect the request to a different page or URL using 'context.Response.Redirect(').
   • Deny access to the request by setting an appropriate status code on the response ('context.Response.StatusCode').
   • Modify the route parameters or URL segments.
   • Perform custom request validation or filtering.
   • Set response headers based on the incoming request.
   • Conditionally modify or customize the request based on specific criteria.
4. Deploy and register your custom HTTP module in the application's web.config file:

   
   
       <system.webServer>
           <modules>
               <add name="CustomModule" type="Namespace.CustomModule" />
           </modules>
       </system.webServer>
   
   

   Replace "Namespace.CustomModule" with the actual namespace and class name of your custom module.

By implementing the appropriate event handlers and logic within your HTTP module, you can intercept incoming requests and modify them before they are further processed by the ASP.NET application. This allows you to customize request handling, perform additional validations or filtering, enforce security measures, or redirect requests based on specific criteria.