General jQuery based approach in frontend is working.

src/site/controllers/parts.json.php

@@ -0,0 +1,59 @@
+<?php
+
+use Joomla\CMS\MVC\Controller\BaseController;
+use Joomla\CMS\Response\JsonResponse;
+use Joomla\CMS\Factory;
+
+// No direct access.
+defined('_JEXEC') or die;
+
+abstract class UserException extends Exception {}
+class InvalidUserDataException extends UserException {}
+
+class ClubsControllerParts extends BaseController
+{
+    
+    public function edit()
+    {
+        $auth = new ClubsHelperAuth();
+        $user = $auth->getCurrentUser();
+        $app = Factory::getApplication();
+        $post = $app->input->post;
+        
+        try
+        {
+            $ret = $this->callMethod($user, $post);
+            echo new JsonResponse($ret);
+        }
+        catch(UserException $e)
+        {
+            echo new JsonResponse($e);
+        }
+        
+    }
+    
+    /**
+     * @param CommonClubsModelUser $user
+     * @param JInput $post
+     */
+    private function callMethod($user, $post)
+    {
+        switch($post->getCmd('partname'))
+        {
+            case 'user.name':
+                return $this->editUserName($user, $post);
+        }
+    }
+    
+    private function editUserName($user, $post)
+    {
+        $name = $post->getString('name');
+        if(strlen($name) < 5)
+            throw new InvalidUserDataException("Der Name muss mindestens 5 Zeichen lang sein.");
+        
+        $user->setName($name);
+        $user->save();
+        $this->setRedirect('index.php?option=com_clubs&view=mypage&layout=parts&type=name');
+    }
+    
+}