Magento admin login through bootstrapped script

admin-login.php

<?php
require_once 'app/Mage.php';
umask(0);
$app = Mage::app('default');

Mage::getSingleton('core/session', array('name' => 'adminhtml'));

// supply username
$user = Mage::getModel('admin/user')->loadByUsername('adminusername');

if (Mage::getSingleton('adminhtml/url')->useSecretKey()) {
  Mage::getSingleton('adminhtml/url')->renewSecretUrls();
}

$session = Mage::getSingleton('admin/session');
$session->setIsFirstVisit(true);
$session->setUser($user);
$session->setAcl(Mage::getResourceModel('admin/acl')->loadAcl());
Mage::dispatchEvent('admin_session_user_login_success',array('user'=>$user));

if ($session->isLoggedIn()) {
  echo("logged in");
}