Fix: DateTime passed to bitpay API weren't assumed UTC, remove DateTime.Now references (#3206)

BTCPayServer/ModelBinders/BitpayDateTimeOffsetModelBinder.cs

@@ -0,0 +1,41 @@
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.Linq;
+using System.Reflection;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Mvc.ModelBinding;
+using Microsoft.VisualBasic.CompilerServices;
+
+namespace BTCPayServer.ModelBinders
+{
+    public class BitpayDateTimeOffsetModelBinder : IModelBinder
+    {
+        public Task BindModelAsync(ModelBindingContext bindingContext)
+        {
+            if (!typeof(DateTimeOffset).GetTypeInfo().IsAssignableFrom(bindingContext.ModelType) &&
+                !typeof(DateTimeOffset?).GetTypeInfo().IsAssignableFrom(bindingContext.ModelType))
+            {
+                return Task.CompletedTask;
+            }
+            ValueProviderResult val = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);
+            string v = val.FirstValue as string;
+            if (v == null)
+            {
+                return Task.CompletedTask;
+            }
+
+            try
+            {
+                var sec = DateTimeOffset.ParseExact(v, "MM/dd/yyyy", CultureInfo.InvariantCulture, DateTimeStyles.AssumeUniversal);
+                bindingContext.Result = ModelBindingResult.Success(sec);
+            }
+            catch
+            {
+                bindingContext.Result = ModelBindingResult.Failed();
+                bindingContext.ModelState.AddModelError(bindingContext.ModelName, "Invalid date (MM/dd/yyyy)");
+            }
+            return Task.CompletedTask;
+        }
+    }
+}