added http digest auth to download clients

code/backend/Cleanuparr.Infrastructure/Http/DynamicHttpClientSystem/BasicAuthHttpMessageHandler.cs

@@ -0,0 +1,27 @@
+using System.Net;
+using System.Net.Http.Headers;
+using System.Text;
+
+namespace Cleanuparr.Infrastructure.Http.DynamicHttpClientSystem;
+
+/// <summary>
+/// Sends Basic auth up front for qBittorrent, Deluge and SABnzbd behind a reverse proxy.
+/// Skips requests that already carry an Authorization header.
+/// </summary>
+public sealed class BasicAuthHttpMessageHandler : DelegatingHandler
+{
+    private readonly string _headerValue;
+
+    public BasicAuthHttpMessageHandler(NetworkCredential credential)
+    {
+        string raw = $"{credential.UserName}:{credential.Password}";
+        _headerValue = Convert.ToBase64String(Encoding.UTF8.GetBytes(raw));
+    }
+
+    protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
+    {
+        request.Headers.Authorization ??= new AuthenticationHeaderValue("Basic", _headerValue);
+
+        return base.SendAsync(request, cancellationToken);
+    }
+}