Update msal-net-provide-httpclient.md

Author: bgavrilMS

articles/active-directory/develop/msal-net-provide-httpclient.md

@@ -20,6 +20,8 @@ ms.custom: "devx-track-csharp, aaddev"
 # Providing your own HttpClient and proxy using MSAL.NET
 When [initializing a client application](msal-net-initializing-client-applications.md), you can use the `.WithHttpClientFactory method` to provide your own HttpClient.  Providing your own HttpClient enables advanced scenarios such fine-grained control of an HTTP proxy, customizing user agent headers, or forcing MSAL to use a specific HttpClient (for example in ASP.NET Core web apps/APIs).
 
+`HttpClient` is intended to be instantiated once and re-used throughout the life of an application. See [guidance](https://docs.microsoft.com/en-us/dotnet/api/system.net.http.httpclient?view=net-5.0#remarks).
+
 ## Initialize with HttpClientFactory
 The following example shows to create an `HttpClientFactory` and then initialize a public client application with it:
 
@@ -31,5 +33,43 @@ var pca = PublicClientApplicationBuilder.Create(MsalTestConstants.ClientId)
                                         .Build();
 ```
 
+## Example implementation using a proxy
+```csharp
+public class HttpFactoryWithProxy : IMsalHttpClientFactory
+{
+    private static HttpClient _httpClient;
+
+    public HttpFactoryWithProxy()
+    {
+        // Consider using Lazy<T> 
+        if (_httpClient == null) 
+        {
+            var proxy = new WebProxy
+            {
+                Address = new Uri($"http://{proxyHost}:{proxyPort}"),
+                BypassProxyOnLocal = false,
+                UseDefaultCredentials = false,
+                Credentials = new NetworkCredential(
+                    userName: proxyUserName,
+                    password: proxyPassword)
+            };
+
+            // Now create a client handler which uses that proxy
+            var httpClientHandler = new HttpClientHandler
+            {
+                Proxy = proxy,
+            };
+
+            _httpClient = new HttpClient(handler: httpClientHandler);
+        }
+    }
+
+    public HttpClient GetHttpClient()
+    {
+        return _httpClient;
+    }
+}
+```
+
 ## HttpClient and Xamarin iOS
 When using Xamarin iOS, it is recommended to create an `HttpClient` that explicitly uses the `NSURLSession`-based handler for iOS 7 and newer. MSAL.NET automatically creates an `HttpClient` that uses `NSURLSessionHandler` for iOS 7 and newer. For more information, read the [Xamarin iOS documentation for HttpClient](/xamarin/cross-platform/macios/http-stack).