Add authorization for MQTTnet.Server

Source/MQTTnet.Server/Web/authorization_handler.py

@@ -0,0 +1,10 @@
+def handle_authenticate(context):
+    """
+    This function is invoked whenever a user tries to access protected HTTP resources.
+    This function must exist and return a proper value. Otherwise the request is denied.
+    """
+
+    username = context["username"]
+    password = context["password"]
+
+    context["is_authenticated"] = True # Change this to _False_ in case of invalid credentials.