Using Middleware

OpenAPI/kiota/index.yml

@@ -29,6 +29,8 @@ landingContent:
             url: experience.md
           - text: Authentication
             url: authentication.md
+          - text: Middleware
+            url: middleware.md
 
   - title: Get started
     linkLists:

OpenAPI/kiota/middleware.md

@@ -0,0 +1,50 @@
+---
+title: Middleware
+description: Learn about implementing middleware into Kiota.
+author: gpltaylor
+ms.topic: overview
+date: 21/11/2023
+---
+
+# Implementing Middleware
+By registering custom middleware delegates we can perform operations before a request is made. For example, auditing and filtering the request before we send.
+
+## Middleware
+Create your middleware class and add your business requirements. For example you may wish to add custom Headers to the request or filter headers and content.
+
+```
+public class SaveRequestHandler : DelegatingHandler
+{
+    protected override async Task<HttpResponseMessage> SendAsync(
+        HttpRequestMessage request, CancellationToken cancellationToken)
+    {
+        string jsonContent = await request.Content.ReadAsStringAsync();
+        Console.WriteLine($"Request: {jsonContent}");
+
+        return await base.SendAsync(request, cancellationToken);
+    }
+}
+```
+## Register Middleware
+Create a Middleware delegate array and use the existing Middleware already implemented within Kiota.HttpClient that includes existing Delegates like Retry, redirect handling and more.
+
+```
+var delegates = KiotaClientFactory.CreateDefaultHandlers();
+delegates.Add(new SaveRequestHandler());
+```
+Next we create a Delegate chain so middleware is registered in the right order
+
+```
+var handler =
+    KiotaClientFactory.ChainHandlersCollectionAndGetFirstLink(
+        KiotaClientFactory.GetDefaultHttpMessageHandler(),
+        delegates.ToArray());
+```
+
+Finally we create Adapter using our HttpClient that's registered our Middleware. This adapter can then be using when submitting requests. The power of this design means that different adapters/middleware can be used when calling Endpoints and therefore gives flexibility to how and when Middleware is used.
+
+```
+var httpClient = new HttpClient(handler!);
+var adapter = new HttpClientRequestAdapter(authProvider, httpClient:httpClient);
+var client = new PostsClient(adapter);
+```