This can be realized with standard Joomla registration form by changing
/components/com_user/controller.php , function register_save()
and replacing $this->setRedirect('index.php', $message); with
$usersipass['username'] = $user->get('username');
$usersipass['password'] = $password;
$mainframe->redirect( 'index.php' );
Howewer for nBill form it does not work. Itried all types of Advanced PHP code for the form.
How this important thing can be realized?