Use default credentials on http client handler (#414)

MSAL integrated Windows authentication requires using default
credentials. This is done if using MSALs http client factory, so must
explicitly opt into this behavior.

---------

Co-authored-by: John Erickson <jerick@microsoft.com>

CredentialProvider.Microsoft/Util/HttpClientFactory.cs

@@ -2,7 +2,6 @@
 //
 // Licensed under the MIT license.
 
-using System;
 using System.Net.Http;
 using Microsoft.Artifacts.Authentication;
 using IAdalHttpClientFactory = Microsoft.IdentityModel.Clients.ActiveDirectory.IHttpClientFactory;
@@ -21,15 +20,12 @@ namespace NuGetCredentialProvider.Util
 
         static HttpClientFactory()
         {
-            // https://learn.microsoft.com/en-us/dotnet/fundamentals/networking/http/httpclient-guidelines
-#if NETFRAMEWORK
-            var httpClient = new HttpClient();
-#else
-            var httpClient  = new HttpClient(new SocketsHttpHandler
+            var httpClient = new HttpClient(new HttpClientHandler
             {
-                PooledConnectionLifetime = TimeSpan.FromMinutes(15)
+                // This is needed to make IWA work. See:
+                // https://github.com/AzureAD/microsoft-authentication-library-for-dotnet/blob/e15befb5f0a6cf4757c5abcaa6487e28e7ebd1bb/src/client/Microsoft.Identity.Client/PlatformsCommon/Shared/SimpleHttpClientFactory.cs#LL26C1-L27C73
+                UseDefaultCredentials = true
             });
-#endif
 
             httpClientFactory = new(httpClient);
         }