create and insert user from post request body

src/Application/Actions/User/CreateUserAction.php

@@ -11,13 +11,13 @@ class CreateUserAction extends UserAction
     /**
      * {@inheritdoc}
      */
-    protected function action(Request $request): Response
+    protected function action(): Response
     {
-        $parsedRequestBody = $request->getParsedBody();
+        $parsedRequestBody = (array)$this->request->getParsedBody();
 
-        $username =  $parsedRequestBody->username;
-        $firstname = $parsedRequestBody->firstname;
-        $lastname = $parsedRequestBody->lastname;
+        $username =  $parsedRequestBody['username'];
+        $firstname = $parsedRequestBody['firstname'];
+        $lastname = $parsedRequestBody['lastname'];
 
         $user = $this->userRepository->createUser($username, $firstname, $lastname);