Add a Login/Logout Menu Item to WordPress Navigation Menu

This will add a Login or Logout (depending on state) to your WordPress navigation menu. I have one on mine now; makes it easy to quickly log in/out to test things.
Put the following in your child theme’s custom functions PHP file.

add_filter( 'wp_nav_menu_items', 'add_loginout_link', 10, 2 );
function add_loginout_link( $items, $args ) {
     if (is_user_logged_in()) {
$items .= '<li><a href="'. wp_logout_url() .'">Log Out</a></li>';
}
elseif (!is_user_logged_in()) {
$items .= '<li><a href="'. site_url('wp-login.php') .'">Log In</a></li>';
}
return $items;
}