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/RequestDeserializerCallback`1.cs

@@ -0,0 +1,13 @@
+using System.Threading.Tasks;
+
+namespace EmbedIO
+{
+    /// <summary>
+    /// A callback used to deserialize an HTTP request body.
+    /// </summary>
+    /// <typeparam name="TData">The expected type of the deserialized data.</typeparam>
+    /// <param name="context">The <see cref="IHttpContext"/> whose request body is to be deserialized.</param>
+    /// <returns>A <see cref="Task{TResult}">Task</see>, representing the ongoing operation,
+    /// whose result will be the deserialized data.</returns>
+    public delegate Task<TData> RequestDeserializerCallback<TData>(IHttpContext context);
+}