This article shows how to migrate existing ASP.NET [HTTP modules and handlers from system.webserver](/iis/configuration/system.webserver/) to ASP.NET Core [middleware](xref:fundamentals/middleware/index).
1. The [application life cycle](https://msdn.microsoft.com/library/ms227673.aspx), which is a series events fired by ASP.NET: [BeginRequest](/dotnet/api/system.web.httpapplication.beginrequest), [AuthenticateRequest](/dotnet/api/system.web.httpapplication.authenticaterequest), etc. Each module can create a handler for one or more events.
In addition to modules, you can add handlers for the life cycle events to your *Global.asax.cs* file. These handlers run after the handlers in the configured modules.
## From handlers and modules to middleware
**Middleware are simpler than HTTP modules and handlers:**
* Modules, handlers, *Global.asax.cs*, *Web.config* (except for IIS configuration) and the application life cycle are gone
* The roles of both modules and handlers have been taken over by middleware
* Middleware are configured using code rather than in *Web.config*
* [Pipeline branching](xref:fundamentals/middleware/index#middleware-run-map-use) lets you send requests to specific middleware, based on not only the URL but also on request headers, query strings, etc.
* Order of middleware is based on the order in which they're inserted into the request pipeline, while order of modules is mainly based on [application life cycle](https://msdn.microsoft.com/library/ms227673.aspx) events
* See [Create a middleware pipeline with IApplicationBuilder](xref:fundamentals/middleware/index#creating-a-middleware-pipeline-with-iapplicationbuilder)
As shown in the [Middleware](xref:fundamentals/middleware/index) page, an ASP.NET Core middleware is a class that exposes an `Invoke` method taking an `HttpContext` and returning a `Task`. Your new middleware will look like this:
The preceding middleware template was taken from the section on [writing middleware](xref:fundamentals/middleware/index#middleware-writing-middleware).
The *MyMiddlewareExtensions* helper class makes it easier to configure your middleware in your `Startup` class. The `UseMyMiddleware` method adds your middleware class to the request pipeline. Services required by the middleware get injected in the middleware's constructor.
A middleware handles this by not calling `Invoke` on the next middleware in the pipeline. Keep in mind that this doesn't fully terminate the request, because previous middlewares will still be invoked when the response makes its way back through the pipeline.
When you migrate your module's functionality to your new middleware, you may find that your code doesn't compile because the `HttpContext` class has significantly changed in ASP.NET Core. [Later on](#migrating-to-the-new-httpcontext), you'll see how to migrate to the new ASP.NET Core HttpContext.
## Migrating module insertion into the request pipeline
HTTP modules are typically added to the request pipeline using *Web.config*:
Convert this by [adding your new middleware](xref:fundamentals/middleware/index#creating-a-middleware-pipeline-with-iapplicationbuilder) to the request pipeline in your `Startup` class:
The exact spot in the pipeline where you insert your new middleware depends on the event that it handled as a module (`BeginRequest`, `EndRequest`, etc.) and its order in your list of modules in *Web.config*.
As previously stated, there's no application life cycle in ASP.NET Core and the order in which responses are processed by middleware differs from the order used by modules. This could make your ordering decision more challenging.
This middleware is very similar to the middleware corresponding to modules. The only real difference is that here there's no call to `_next.Invoke(context)`. That makes sense, because the handler is at the end of the request pipeline, so there will be no next middleware to invoke.
You could convert this by adding your new handler middleware to the request pipeline in your `Startup` class, similar to middleware converted from modules. The problem with that approach is that it would send all requests to your new handler middleware. However, you only want requests with a given extension to reach your middleware. That would give you the same functionality you had with your HTTP handler.
One solution is to branch the pipeline for requests with a given extension, using the `MapWhen` extension method. You do this in the same `Configure` method where you add the other middleware:
1. A lambda that takes the `HttpContext` and returns `true` if the request should go down the branch. This means you can branch requests not just based on their extension, but also on request headers, query string parameters, etc.
2. A lambda that takes an `IApplicationBuilder` and adds all the middleware for the branch. This means you can add additional middleware to the branch in front of your handler middleware.
Middleware added to the pipeline before the branch will be invoked on all requests; the branch will have no impact on them.
## Loading middleware options using the options pattern
Some modules and handlers have configuration options that are stored in *Web.config*. However, in ASP.NET Core a new configuration model is used in place of *Web.config*.
The options pattern uses ASP.NET Core's dependency injection framework to associate the options type (such as `MyMiddlewareOptions`) with a `MyMiddlewareOptions` object that has the actual options.
The [UseMiddleware](#http-modules-usemiddleware) extension method that adds your middleware to the `IApplicationBuilder` takes care of dependency injection.
The options pattern has the advantage that it creates loose coupling between options values and their consumers. Once you've associated an options class with the actual options values, any other class can get access to the options through the dependency injection framework. There's no need to pass around options values.
This breaks down though if you want to use the same middleware twice, with different options. For example an authorization middleware used in different branches allowing different roles. You can't associate two different options objects with the one options class.
The solution is to get the options objects with the actual options values in your `Startup` class and pass those directly to each instance of your middleware.
2. Retrieve options values and pass them to middleware. The `Use...` extension method (which adds your middleware to the pipeline) is a logical place to pass in the option values:
3. Enable middleware to take an options parameter. Provide an overload of the `Use...` extension method (that takes the options parameter and passes it to `UseMiddleware`). When `UseMiddleware` is called with parameters, it passes the parameters to your middleware constructor when it instantiates the middleware object.
`HttpContext` has significantly changed in ASP.NET Core. This section shows how to translate the most commonly used properties of [System.Web.HttpContext](/dotnet/api/system.web.httpcontext) to the new `Microsoft.AspNetCore.Http.HttpContext`.
The solution is to set a callback method that will be called right before writing to the response starts. This is best done at the start of the `Invoke` method in your middleware. It's this callback method that sets your response headers.
Cookies travel to the browser in a *Set-Cookie* response header. As a result, sending cookies requires the same callback as used for sending response headers:
