refactored incoming signature validator to use form fields instead of httprequest

LiteCharms.Features.MidrandBooks/Payments/PayfastService.cs

@@ -48,13 +48,8 @@ public sealed partial class PayfastService(IDbContextFactory<MidrandBooksDbConte
         }
     }
 
-    public static bool VerifyIncomingSignature(HttpRequest request, string passphrase)
+    public static bool VerifyIncomingSignature(IDictionary<string, string> formFields, string passphrase)
     {
-        var formFields = new Dictionary<string, string>(StringComparer.Ordinal);
-
-        foreach (var file in request.Form)
-            formFields.Add(file.Key, file.Value.ToString());
-
         if (!formFields.TryGetValue("signature", out string? incomingSignature))
             return false;