[wordpress] Block all users except admin (and ajax requests) from dashboard / wp-login

functions.php

<?php
//BLOCK USERS EXCEPT ADMIN FROM DASHBOARD / WP-LOGIN
add_action( 'init', 'blockusers_init' );
function blockusers_init() {
  if ( is_admin() && ! current_user_can( 'administrator' ) &&
  ! ( defined( 'DOING_AJAX' ) && DOING_AJAX ) ) {
    wp_redirect( home_url() );
    exit;
  }
}