How to log into joomla through an external script?

<?php//http://domain.com/script/script.php?username=username&passwd=passworddefine( '_JEXEC', 1 );define('JPATH_BASE', '../' );define( 'DS', DIRECTORY_SEPARATOR );require_once('../configuration.php');require_once ( JPATH_BASE .DS.'includes'.DS.'defines.php' );require_once ( JPATH_BASE .DS.'includes'.DS.'framework.php' );require_once ( JPATH_BASE .DS.'libraries'.DS.'joomla'.DS.'factory.php' );/* Create the Application */$mainframe =& JFactory::getApplication('site');jimport('joomla.plugin.helper');$credentials = array();$credentials['username'] = JRequest::getVar('username', '', 'method', 'username');$credentials['password'] = JRequest::getVar('passwd', '', 'method', 'passwd');//perform the login action$error = $mainframe->login($credentials);$user = JFactory::getUser();//now you are logged in$mainframe->logout();//now you are logged out

For Joomla 3.x below is more clean and helpful. Below codes will does verify hard-coded username and password. If user is existing, it will be redirected to the index.php page.

<?php/** * Joomla! External authentication script * * @author vdespa * Version 1.0 * * Code adapted from /index.php * * @package    Joomla.Site * * @copyright  Copyright (C) 2005 - 2014 Open Source Matters, Inc. All rights reserved. * @license    GNU General Public License version 2 or later; see LICENSE.txt */if (version_compare(PHP_VERSION, '5.3.1', '<')){    die('Your host needs to use PHP 5.3.1 or higher to run this version of Joomla!');}/** * Constant that is checked in included files to prevent direct access. * define() is used in the installation folder rather than "const" to not error for PHP 5.2 and lower */define('_JEXEC', 1);if (file_exists(__DIR__ . '/defines.php')){    include_once __DIR__ . '/defines.php';}if (!defined('_JDEFINES')){    define('JPATH_BASE', __DIR__);    require_once JPATH_BASE . '/includes/defines.php';}require_once JPATH_BASE . '/includes/framework.php';// Instantiate the application.$app = JFactory::getApplication('site');jimport('joomla.plugin.helper');// JFactoryrequire_once (JPATH_BASE .'/libraries/joomla/factory.php');// Hardcoded for now$credentials['username'] = 'admin';$credentials['password'] = 'admin';// Get a database object$db    = JFactory::getDbo();$query = $db->getQuery(true)    ->select('id, password')    ->from('#__users')    ->where('username=' . $db->quote($credentials['username']));$db->setQuery($query);$result = $db->loadObject();if ($result){    $match = JUserHelper::verifyPassword($credentials['password'], $result->password, $result->id);    if ($match === true)    {        // Bring this in line with the rest of the system        $user = JUser::getInstance($result->id);        echo 'Joomla! Authentication was successful!' . '<br>';        echo 'Joomla! Token is:' . JHTML::_( 'form.token' );    //perform the login action    $error = $app->login($credentials);    $logged_user = JFactory::getUser();    var_dump($logged_user );    //redirect logged in user    $app->redirect('index.php');    }    else    {        // Invalid password        // Prmitive error handling        echo 'Joomla! Token is:' . JHTML::_( 'form.token' ) . '<br>';        die('Invalid password');    }} else {    // Invalid user    // Prmitive error handling    die('Cound not find user in the database');}

I would suggest one of the following solutions:

• Write a login plugin specific to your script.
• Using CURL in your script to do a POST-Request on the normal login form (CURL can cope cookies, too.)
• (Simplest): Do not authenticate by Joomla!, but by .htaccess.