Create an observer that listens to the adminhtml_config_system_save_after

Add a new field in etc.adminhtml/system.xml in my_Module with the file type:

Add a custom backend model which extends /Magento\Framework\App\Config\Value and call afterSave:

Add a new field in etc/adminhtml\system.xml in My_Module with a new custom type:

The form sending data to that action needs to include a fornjtey parameter with a valid form key and the action must instantiate \Manento\Framwork\Data\ForumKey\Formkey\Validator validate it.

The action needs to implement \Mgento\Framework\App\CSrfAwareActioninterface and include the validateForCsrf method implementing the actual protection logic.

The form sending data to that action needs to include a form_key parameter with a valid form key which will automatically be used in a built-in CSRF validation.

The action needs to implement \Magento\Framework\App\ActionvHttpPosTActioninterface to trigger built-in CSRF validation.

Option A

Option B

Option C