Added application and project roles validation for API procedure calls

app/Api/Authorization/SubtaskAuthorization.php

@@ -0,0 +1,19 @@
+<?php
+
+namespace Kanboard\Api\Authorization;
+
+/**
+ * Class SubtaskAuthorization
+ *
+ * @package Kanboard\Api\Authorization
+ * @author  Frederic Guillot
+ */
+class SubtaskAuthorization extends ProjectAuthorization
+{
+    public function check($class, $method, $subtask_id)
+    {
+        if ($this->userSession->isLogged()) {
+            $this->checkProjectPermission($class, $method, $this->subtaskModel->getProjectId($subtask_id));
+        }
+    }
+}