Add authorization for MQTTnet.Server

Source/MQTTnet.Server/Web/Extensions.cs

@@ -0,0 +1,20 @@
+using System;
+using System.IO;
+using System.Text;
+using Microsoft.AspNetCore.Http;
+
+namespace MQTTnet.Server.Web
+{
+    public static class Extensions
+    {
+        public static string ReadBodyAsString(this HttpRequest request)
+        {
+            if (request == null) throw new ArgumentNullException(nameof(request));
+
+            using (var reader = new StreamReader(request.Body, Encoding.UTF8))
+            {
+                return reader.ReadToEnd();
+            }
+        }
+    }
+}