Use this to add custom fields or validation logic (e.g., matching a secondary database). 💻 Code Example: hook_user_presave
Inside presave , always call $user->isNew() to ensure your code only runs during initial registration rather than every time a profile is updated. drupal-8-user-register-hook
If you need to stop registration based on custom business logic (e.g., checking an external blacklist), use a custom validation handler via hook_form_alter . Use this to add custom fields or validation logic (e
Best for modifying data (e.g., adding a default role) before it hits the database. Runs after the user is created. checking an external blacklist)