WordPress at a glance
function is not described

wp_ajax_logged_in() WP 3.4.0

Ajax handler for Customizer preview logged-in status.

No Hooks.

Return

Nothing (null).

Usage

wp_ajax_logged_in();

Code of wp ajax logged in: wp-admin/includes/ajax-actions.php VER 5.0.3

<?php
function wp_ajax_logged_in() {
	wp_die( 1 );
}