Mine

<?php
if (!isset($_SESSION['log_out_user']))
{
	unset($_SERVER['AUTH_USER']);
	$_SESSION['log_out_user'] = TRUE;
}

if(!isset($_SERVER['AUTH_USER']))
{
	header('WWW-Authenticate: Basic realm="' . your_auth_realm_here . '"');
	header('HTTP/1.0 401 Unauthorized');
	echo('This is for authorized users only.');
	exit;
} else {
	unset($_SESSION);
	header('Location: ' . $somewhere_else);
	exit;
}
?>