Refactor HttpClient usage and NTLM auth handling

Centralize HttpClient configuration using IHttpClientFactory with a named "Default" client. Move NTLM authentication logic from HttpClientHandler to request-level options, improving testability and aligning with .NET best practices.

src/ReC.Application/DependencyInjection.cs

@@ -1,10 +1,10 @@
-using MediatR;
+using FluentValidation;
+using MediatR;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 using ReC.Application.Common.Behaviors;
 using ReC.Application.Common.Options;
 using System.Reflection;
-using FluentValidation;
 
 namespace ReC.Application;
 
@@ -35,7 +35,11 @@ public static class DependencyInjection
             cfg.LicenseKey = configOpt.LuckyPennySoftwareLicenseKey;
         });
 
-        services.AddHttpClient();
+        services.AddHttpClient("Default")
+            .ConfigurePrimaryHttpMessageHandler(() => new HttpClientHandler
+            {
+                UseDefaultCredentials = false
+            });
 
         return services;
     }

src/ReC.Application/RecActions/Commands/InvokeRecActionCommand.cs

@@ -31,16 +31,7 @@ public class InvokeRecActionCommandHandler(
     {
         var action = request.Action;
 
-        var handler = new HttpClientHandler();
-        if (action.EndpointAuthType == "NTLM Auth" && !string.IsNullOrWhiteSpace(action.EndpointAuthUsername))
-        {
-            handler.Credentials = new NetworkCredential(
-                action.EndpointAuthUsername,
-                action.EndpointAuthPassword,
-                action.EndpointAuthDomain);
-        }
-        
-        using var http = new HttpClient(handler);
+        using var http = clientFactory.CreateClient("Default");
 
         if (action.RestType is null)
             throw new DataIntegrityException(
@@ -53,7 +44,7 @@ public class InvokeRecActionCommandHandler(
             .ToHttpMethod()
             .ToHttpRequestMessage(action.EndpointUri);
 
-        if(action.Body is not null)
+        if (action.Body is not null)
         {
             using var reqBody = new StringContent(action.Body);
             httpReq.Content = reqBody;
@@ -100,10 +91,17 @@ public class InvokeRecActionCommandHandler(
                     httpReq.Headers.Authorization = new AuthenticationHeaderValue("Basic", basicAuth);
                 }
                 break;
-            
+
             case "NTLM Auth":
-                // NTLM authentication is configured on the HttpClientHandler before creating the HttpClient.
-                // No additional action is needed here.
+                if (!string.IsNullOrWhiteSpace(action.EndpointAuthUsername))
+                {
+                    var credentials = new NetworkCredential(
+                        action.EndpointAuthUsername,
+                        action.EndpointAuthPassword,
+                        action.EndpointAuthDomain);
+                    var credentialCache = new CredentialCache { { httpReq.RequestUri!, "NTLM", credentials } };
+                    httpReq.Options.Set(new HttpRequestOptionsKey<CredentialCache>("Credentials"), credentialCache);
+                }
                 break;
 
             case "Digest Auth":