thefuxia/t5-nav-menu-log-in.php

## t5-nav-menu-log-in.php
<?php
/**
 * Plugin Name: T5 Nav Menu Log-in Link
 * Description: Adds a log-in or log-out link to the first level of the first nav menu
 * Plugin URI:  http://wordpress.stackexchange.com/q/77614
 * Version:     2012.12.30
 * Author:      Fuxia Scholz
 * Author URI:  https://fuxia.me
 * Licence:     MIT
 * License URI: http://opensource.org/licenses/MIT
 */

add_filter( 'wp_nav_menu_objects', 't5_menu_log_link', 100, 2 );

/**
 * Add a link to the nav menu.
 *
 * @wp-hook wp_nav_menu_objects
 * @param  array  $sorted_menu_items Existing nav menu items
 * @param  object $args Nav menu arguments. If $args->add_loginout is FALSE,
 *                      the function does nothing.
 * @return array  Nav menu items
 */
function t5_menu_log_link( $sorted_menu_items, $args )
{
	static $done = FALSE;

	if ( ! isset ( $args->add_loginout ) && $done )
		return $sorted_menu_items;

	if ( isset ( $args->add_loginout ) && ! $args->add_loginout )
		return $sorted_menu_items;

	$done = TRUE;
	$here = esc_url( home_url( $_SERVER['REQUEST_URI'] ) );

	$link                   = new stdClass;
	$link->menu_item_parent = 0;
	$link->ID               = '';
	$link->db_id            = '';

	if ( is_user_logged_in() )
	{
		$link->url   = wp_logout_url( $here );
		$link->title = __( 'Log Out' );
	}
	else
	{
		$link->url   = wp_login_url( $here );
		$link->title = __( 'Log In' );
	}

	$sorted_menu_items[] = $link;

	return $sorted_menu_items;
}