Got at least one data fetching method working; turns out, we can't use a patched LogicStack to get the data

Vendor/EmbedIO-3.5.2/WebApi/JsonDataAttribute.cs

@@ -0,0 +1,40 @@
+using System;
+using System.Threading.Tasks;
+
+namespace EmbedIO.WebApi
+{
+    /// <summary>
+    /// <para>Specifies that a parameter of a controller method will receive
+    /// an object obtained by deserializing the request body as JSON.</para>
+    /// <para>The received object will be <see langword="null"/>
+    /// only if the deserialized object is <c>null</c>.</para>
+    /// <para>If the request body is not valid JSON,
+    /// or if it cannot be deserialized to the type of the parameter,
+    /// a <c>400 Bad Request</c> response will be sent to the client.</para>
+    /// <para>This class cannot be inherited.</para>
+    /// </summary>
+    /// <seealso cref="Attribute" />
+    /// <seealso cref="IRequestDataAttribute{TController}" />
+    [AttributeUsage(AttributeTargets.Parameter)]
+    public class JsonDataAttribute : Attribute, IRequestDataAttribute<WebApiController>
+    {
+        /// <inheritdoc />
+        public async Task<object?> GetRequestDataAsync(WebApiController controller, Type type, string parameterName)
+        {
+            string body;
+            using (var reader = controller.HttpContext.OpenRequestText())
+            {
+                body = await reader.ReadToEndAsync().ConfigureAwait(false);
+            }
+
+            try
+            {
+                return Swan.Formatters.Json.Deserialize(body, type);
+            }
+            catch (FormatException)
+            {
+                throw HttpException.BadRequest($"Expected request body to be deserializable to {type.FullName}.");
+            }
+        }
+    }
+}