lib.php

<?php
/**
 * Mahara: Electronic portfolio, weblog, resume builder and social networking
 * Copyright (C) 2006-2007 Catalyst IT Ltd (http://www.catalyst.net.nz)
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 * @package    mahara
 * @subpackage auth
 * @author     Nigel McNie <nigel@catalyst.net.nz>
 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL
 * @copyright  (C) 2006,2007 Catalyst IT Ltd http://catalyst.net.nz
 *
 */

defined('INTERNAL') || die();

require('session.php');
require(get_config('docroot') . 'auth/user.php');

/**
 * Unknown user exception
 */
class AuthUnknownUserException extends UserException {}

/**
 * We tried to call a method on an auth plugin that hasn't been init'ed 
 * successfully
 */
class UninitialisedAuthException extends SystemException {}

/**
 * Base authentication class. Provides a common interface with which
 * authentication can be carried out for system users.
 *
 * @todo for authentication:
 *   - inactivity: each institution has inactivity timeout times, this needs
 *     to be supported
 *     - this means the lastlogin field needs to be updated on the usr table
 *     - warnings are handled by cron
 */
abstract class Auth {

    protected $instanceid;
    protected $institution;
    protected $instancename;
    protected $priority;
    protected $authname;
    protected $config;
    protected $has_instance_config;
    protected $type;
    protected $ready;

    /**
     * Given an id, create the auth object and retrieve the config settings
     * If an instance ID is provided, get all the *instance* config settings
     *
     * @param  int  $id   The unique ID of the auth instance
     * @return bool       Whether the create was successful
     */
    public function __construct($id = null) {
        $this->ready = false;
    }

    /**
     * Instantiate the plugin by pulling the config data for an instance from
     * the database
     *
     * @param  int  $id   The unique ID of the auth instance
     * @return bool       Whether the create was successful
     */
    public function init($id) {
        if (!is_numeric($id) || intval($id) != $id) {
            throw new UserNotFoundException();
        }

        $instance = get_record('auth_instance', 'id', $id);
        if (empty($instance)) {
            throw new UserNotFoundException();
        }

        $this->instanceid   = $id;
        $this->institution  = $instance->institution;
        $this->instancename = $instance->instancename;
        $this->priority     = $instance->priority;
        $this->authname     = $instance->authname;

        // Return now if the plugin type doesn't require any config 
        // (e.g. internal)
        if ($this->has_instance_config == false) {
            return true;
        }

        $records = get_records_array('auth_instance_config', 'instance', $this->instanceid);

        if ($records == false) {
            return false;
        }

        foreach($records as $record) {
            $this->config[$record->field] = $record->value;
        }

        return true;
    }

    /**
     * The __get overloader is invoked when the requested member is private or
     * protected, or just doesn't exist.
     * 
     * @param  string  $name   The name of the value to fetch
     * @return mixed           The value
     */
    public function __get($name) {
        $approved_members = array('instanceid', 'institution', 'instancename', 'priority', 'authname', 'type');

        if (in_array($name, $approved_members)) {
            return $this->{$name};
        }

        if (isset($this->config['name'])) {
            return $this->config['name'];
        }
        return null;
    }

    /**
     * The __set overloader is invoked when the specified member is private or
     * protected, or just doesn't exist.
     * 
     * @param  string  $name   The name of the value to set
     * @param  mixed   $value  The value to assign
     * @return void
     */
    public function __set($name, $value) {
        /*
        if (property_exists($this, $name)) {
            $this->{$name} = $value;
            return;
        }
        */
        throw new SystemException('It\'s forbidden to set values on Auth objects');
    }

    /**
     * Check that the plugin has been initialised before we try to use it.
     * 
     * @throws UninitialisedAuthException
     * @return bool 
     */
    protected function must_be_ready() {
        if ($this->ready == false) {
            throw new UninitialisedAuthException('This Auth plugin has not been initialised');
        }
        return true;
    }

    /**
     * Fetch the URL that users can visit to change their passwords. This might
     * be a Moodle installation, for example.
     * 
     * @return  mixed   URL to change password or false if there is none
     */
    public function changepasswordurl() {
        $this->must_be_ready();
        if (empty($this->config['changepasswordurl'])) {
            return false;
        }
        return $this->config['changepasswordurl'];
    }

    /**
     * Given a username and password, attempts to log the user in.
     *
     * @param object $user      An object with username member (at least)
     * @param string $password  The password to use for the attempt
     * @return bool             Whether the authentication was successful
     * @throws AuthUnknownUserException  If the user is unknown to the
     *                                   authentication method
     */
    public function authenticate_user_account($user, $password) {
        $this->must_be_ready();
        return false;
    }

    /**
     * Given a username, returns whether the user exists in the usr table
     *
     * @param string $username The username to attempt to identify
     * @return bool            Whether the username exists
     */
    public function user_exists($username) {
        $this->must_be_ready();
        if (record_exists('usr', 'LOWER(username)', strtolower($username))) {
            return true;
        }
        throw new AuthUnknownUserException("\"$username\" is not known to Auth");
    }

    /**
     * Given a username, returns a hash of information about a user from the
     * external data source, e.g. Moodle or Drupal.
     *
     * @param string $username The username to look up information for
     * @return array           The information for the user
     * @throws AuthUnknownUserException If the user is unknown to the
     *                                  authentication method
     */
    public function get_user_info($username) {
        return false;
    }

    /**
     * Given a username, return information about the user from the database.
     * This object must_be_ready, which means it will have an authinstanceid. 
     * This is used to disambiguate between users with the same username.
     *
     * The information retrieved must be all rows in the user table, with the
     * timestamps formatted as unix timestamps. An example (taken from the
     * internal authentication mechanism, which allows usernames to be case
     * insensitive):
     *
     * <code>
     * get_record('usr', 'LOWER(username)', strtolower($username), null, null, null, null,
     *    '*, ' . db_format_tsfield('expiry') . ', ' . db_format_tsfield('lastlogin'));
     * </code>
     *
     * @param string $username The username to get information for
     * @return array           Data that can be used to populate the session
     * @throws AuthUnknownUserException If the user is unknown to the
     *                                  authentication method
     */
    public function get_user_info_cached($username) {
        $this->must_be_ready();
        if (!$result = get_record('usr', 'LOWER(username)', strtolower($username), null, null, null, null,
                    '*, ' . db_format_tsfield('expiry') . ', ' . db_format_tsfield('lastlogin'))) {
            throw new AuthUnknownUserException("\"$username\" is not known to AuthInternal");
        }
        $cache[$result->username] = $result;
        return $result;
    }

    /**
     * Given a password, returns whether it is in a valid format for this
     * authentication method.
     *
     * This only needs to be defined by subclasses if:
     *  - They implement the change_password method, which means that the
     *    system can use the <kbd>passwordchange</kbd> flag on the <kbd>usr</kbd>
     *    table to control whether the user's password needs changing.
     *  - The password that a user can set must be in a certain format.
     *
     * The default behaviour is to assume that the password is in a valid form,
     * so make sure to implement this method if this is not the case!
     *
     * This method is defined to be empty, so that authentication methods do 
     * not have to specify a format if they do not need to.
     *
     * @param string $password The password to check
     * @return bool            Whether the username is in valid form.
     */
    public function is_password_valid($password) {
        return true;
    }

}


/******************************************************************************/
    // End of Auth base-class
/******************************************************************************/

/**
 * Handles authentication by setting up a session for a user if they are logged 
 * in.
 *
 * This function combined with the Session class is smart - if the user is not
 * logged in then they do not get a session, which prevents simple curl hits
 * or search engine crawls to a page from getting sessions they won't use.
 *
 * Once the user has a session, they keep it even if the log out, so it can
 * be reused. The session does expire, but the expiry time is typically a week
 * or more.
 *
 * If the user is not authenticated for this page, then this function will
 * exit, printing the login page. Therefore, after including init.php, you can
 * be sure that the user is logged in, or has a valid guest key. However, no
 * testing is done to make sure the user has the required permissions to see
 * the page.
 *
 */
function auth_setup () {
    global $SESSION, $USER;

    // If the system is not installed, let the user through in the hope that
    // they can fix this little problem :)
    if (!get_config('installed')) {
        $USER->logout();
        return;
    }

    // Check the time that the session is set to log out. If the user does
    // not have a session, this time will be 0.
    $sessionlogouttime = $USER->get('logout_time');
    if ($sessionlogouttime && isset($_GET['logout'])) {
        $USER->logout();
        $SESSION->add_ok_msg(get_string('loggedoutok'));
        redirect();
    }
    if ($sessionlogouttime > time()) {
        // The session is still active, so continue it.
        // Make sure that if a user's admin status has changed, they're kicked
        // out of the admin section
        if (defined('ADMIN')) {
            $userreallyadmin = get_field('usr', 'admin', 'id', $USER->id);
            if (!$USER->get('admin') && $userreallyadmin) {
                // The user has been made into an admin
                $USER->admin = 1;
            }
            else if ($USER->get('admin') && !$userreallyadmin) {
                // The user's admin rights have been taken away
                $USER->admin = 0;
            }
            if (!$USER->get('admin')) {
                $SESSION->add_error_msg(get_string('accessforbiddentoadminsection'));
                redirect();
            }
        } else if (defined('INSTITUTIONALADMIN') && !$USER->get('admin')) {
            $userreallyadminfor = get_column('usr_institution', 'institution', 'usr', $USER->id, 'admin', 1);
            if (!$USER->is_institutional_admin() && !empty($userreallyadminfor)) {
                $USER->set_admin_institutions($userreallyadminfor);
            }
            else if ($USER->is_institutional_admin() && empty($userreallyadminfor)) {
                $USER->set_admin_institutions(array());
            }
            if (!$USER->is_institutional_admin()) {
                $SESSION->add_error_msg(get_string('accessforbiddentoadminsection'));
                redirect();
            }
        }
        $USER->renew();
        auth_check_password_change();
    }
    else if ($sessionlogouttime > 0) {
        // The session timed out
        $USER->logout();

        if (defined('JSON')) {
            json_reply('global', get_string('sessiontimedoutreload'), 1);
        }

        // If the page the user is viewing is public, inform them that they can
        // log in again
        if (defined('PUBLIC')) {
            // @todo this links to ?login - later it should do magic to make
            // sure that whatever GET string is made it includes the old data
            // correctly
            $SESSION->add_info_msg(get_string('sessiontimedoutpublic'), false);
            return;
        }

        auth_draw_login_page(get_string('sessiontimedout'));
    }
    else {
        // There is no session, so we check to see if one needs to be started.
        // Build login form. If the form is submitted it will be handled here,
        // and set $USER for us (this will happen when users hit a page and
        // specify login data immediately
        require_once('pieforms/pieform.php');
        $form = new Pieform(auth_get_login_form());
        if ($USER->is_logged_in()) {
            return;
        }
        
        // Check if the page is public or the site is configured to be public.
        if (defined('PUBLIC') && !isset($_GET['login'])) {
            return;
        }

        // No session and a json request
        if (defined('JSON')) {
            json_reply('global', get_string('nosessionreload'), 1);
        }
        
        auth_draw_login_page(null, $form);
        exit;
    }
}

/**
 * 
 * Returns all auth instances
 *
 * @return array                     Array of auth instance records
 */
function auth_get_auth_instances() {
    static $cache = array();

    if (count($cache) > 0) {
        return $cache;
    }

    $sql ='
        SELECT DISTINCT
            i.id,
            inst.name,
            inst.displayname,
            i.instancename,
            i.authname
        FROM 
            {institution} inst,
            {auth_instance} i
        WHERE 
            i.institution = inst.name
        ORDER BY
            inst.displayname,
            i.instancename';

    $cache = get_records_sql_array($sql, array());

    if (empty($cache)) {
        return array();
    }

    return $cache;
}


/**
 * 
 * Given a list of institutions, returns all auth instances associated with them
 *
 * @return array                     Array of auth instance records
 */
function auth_get_auth_instances_for_institutions($institutions) {
    if (empty($institutions)) {
        return array();
    }
    $sql ='
        SELECT DISTINCT
            i.id,
            inst.name,
            inst.displayname,
            i.instancename
        FROM 
            {institution} inst,
            {auth_instance} i
        WHERE 
            i.institution = inst.name AND
            inst.name IN (' . join(',', array_map('db_quote',$institutions)) . ')
        ORDER BY
            inst.displayname,
            i.instancename';

    return get_records_sql_array($sql, array());
}


/**
 * Given an institution, returns the authentication methods used by it, sorted 
 * by priority.
 *
 * @param  string   $institution     Name of the institution
 * @return array                     Array of auth instance records
 */
function auth_get_auth_instances_for_institution($institution=null) {
    static $cache = array();

    if (null == $institution) {
        return array();
    }

    if (!isset($cache[$institution])) {
        // Get auth instances in order of priority
        // DO NOT CHANGE THE SORT ORDER OF THIS RESULT SET
        // YEAH EINSTEIN - THAT MEANS YOU!!!

        // TODO: work out why this won't accept a placeholder - had to use db_quote
        $sql ='
            SELECT DISTINCT
                i.id,
                i.instancename,
                i.priority,
                i.authname,
                a.requires_config,
                a.requires_parent
            FROM 
                {auth_instance} i,
                {auth_installed} a
            WHERE 
                a.name = i.authname AND
                i.institution = '. db_quote($institution).'
            ORDER BY
                i.priority,
                i.instancename';

        $cache[$institution] = get_records_sql_array($sql, array());

        if (empty($cache[$institution])) {
            return false;
        }
    }

    return $cache[$institution];
}

/**
 * Given a wwwroot, find any auth instances that can come from that host
 * 
 * @param   string  wwwroot of the host that is connecting to us
 * @return  array   array of record objects
 */
function auth_get_auth_instances_for_wwwroot($wwwroot) {

    // TODO: we just need ai.id and ai.authname... rewrite query, or
    // just drop this function
    $query = "  SELECT
                    ai.*,
                    aic.*,
                    i.*
                FROM
                    {auth_instance} ai, 
                    {auth_instance_config} aic,
                    {institution} i
                WHERE
                    aic.field = 'wwwroot' AND
                    aic.value = ? AND
                    aic.instance = ai.id AND
                    i.name = ai.institution";

    return get_records_sql_array($query, array('value' => $wwwroot));
}

/**
 * Given an institution, returns the authentication methods used by it, sorted 
 * by priority.
 *
 * @param  string   $institution     Name of the institution
 * @return array                     Array of auth instance records
 */
function auth_get_auth_instances_for_username($institution, $username) {
    static $cache = array();

    if (!isset($cache[$institution][$username])) {
        // Get auth instances in order of priority
        // DO NOT CHANGE THE SORT ORDER OF THIS RESULT SET
        // YEAH EINSTEIN - THAT MEANS YOU!!!

        // TODO: work out why this won't accept a placeholder - had to use db_quote
        $sql ='
            SELECT DISTINCT
                i.id,
                i.instancename,
                i.priority,
                i.authname,
                a.requires_config,
                a.requires_parent
            FROM 
                {auth_instance} i,
                {auth_installed} a,
                {usr} u
            WHERE 
                a.name = i.authname AND
                i.institution = ? AND
                u.username = ? AND
                u.institution = i.institution
            ORDER BY
                i.priority,
                i.instancename';

        $cache[$institution][$username] = get_records_sql_array($sql, array(array('institution' => $institution), array('username' => $username)));

        if (empty($cache[$institution])) {
            return false;
        }
    }

    return $cache[$institution];
}

/**
 * Given an institution, get all the auth types EXCEPT those that are already 
 * enabled AND do not require configuration.
 *
 * @param  string   $institution     Name of the institution
 * @return array                     Array of auth instance records
 */
function auth_get_available_auth_types($institution=null) {

    if (!is_null($institution) && (!is_string($institution) || strlen($institution) > 255)) {
        return array();
    }

    // TODO: work out why this won't accept a placeholder - had to use db_quote
    $sql ='
        SELECT DISTINCT
            a.name,
            a.requires_config
        FROM 
            {auth_installed} a
        LEFT JOIN 
            {auth_instance} i
        ON 
            a.name = i.authname AND
            i.institution = '. db_quote($institution).'
        WHERE
           (a.requires_config = 1 OR
            i.id IS NULL) AND
            a.active = 1
        ORDER BY
            a.name';          

    if (is_null($institution)) {
        $result = get_records_array('auth_installed', '','','name','name, requires_config');
    } else {
        $result = get_records_sql_array($sql, array());
    }

    if (empty($result)) {
        return array();
    }

    return $result;
}

/**
 * Checks whether the current user needs to change their password, and handles
 * the password changing if it's required.
 *
 * This only applies for the internal authentication plugin. Other plugins
 * will, in theory, have different data stores, making changing the password
 * via the internal form difficult.
 */
function auth_check_password_change() {
    global $USER;
    if (!$USER->get('passwordchange')) {
        return;
    }

    $authobj = AuthFactory::create($USER->authinstance);

    if ($authobj->changepasswordurl) {
        redirect($authobj->changepasswordurl);
        exit;
    }

    // @todo auth preference for a password change screen for all auth methods other than internal
    if (method_exists($authobj, 'change_password')) {

        require_once('pieforms/pieform.php');
        $form = array(
            'name'       => 'change_password',
            'method'     => 'post',
            'plugintype' => 'auth',
            'pluginname' => 'internal',
            'elements'   => array(
                'password1' => array(
                    'type'        => 'password',
                    'title'       => get_string('newpassword') . ':',
                    'description' => get_string('yournewpassword'),
                    'rules'       => array(
                        'required' => true
                    )
                ),
                'password2' => array(
                    'type'        => 'password',
                    'title'       => get_string('confirmpassword') . ':',
                    'description' => get_string('yournewpasswordagain'),
                    'rules'       => array(
                        'required' => true,
                    ),
                ),
                'email' => array(
                    'type'   => 'text',
                    'title'  => get_string('principalemailaddress', 'artefact.internal'),
                    'ignore' => (trim($USER->get('email')) != '' && !preg_match('/@example\.org$/', $USER->get('email'))),
                    'rules'  => array(
                        'required' => true,
                        'email'    => true,
                    ),
                ),
                'submit' => array(
                    'type'  => 'submit',
                    'value' => get_string('changepassword'),
                ),
            )
        );

        $smarty = smarty();
        $smarty->assign('change_password_form', pieform($form));
        $smarty->display('change_password.tpl');
        exit;
    }
}

/**
 * Validates the form for changing the password for a user.
 *
 * Change password will only be if a URL for it exists, or a function exists.
 *
 * @param Pieform  $form   The form to check
 * @param array    $values The values to check
 */
function change_password_validate(Pieform $form, $values) {
    global $USER;

    // Get the authentication type for the user, and
    // use the information to validate the password
    $authobj = AuthFactory::create($USER->authinstance);

    // @todo this could be done by a custom form rule... 'password' => $user
    password_validate($form, $values, $USER);

    // The password cannot be the same as the old one
    if (!$form->get_error('password1')
        && $authobj->authenticate_user_account($USER, $values['password1'])) {
        $form->set_error('password1', get_string('passwordnotchanged'));
    }
}

/**
 * Changes the password for a user, given that it is valid.
 *
 * @param array $values The submitted form values
 */
function change_password_submit(Pieform $form, $values) {
    global $USER, $SESSION;

    $authobj = AuthFactory::create($USER->authinstance);

    // This method should exist, because if it did not then the change
    // password form would not have been shown.
    if ($password = $authobj->change_password($USER, $values['password1'])) {
        $SESSION->add_ok_msg(get_string('passwordsaved'));
        if (!empty($values['email'])) {
            $USER->email = $values['email'];
            $USER->commit();
            set_profile_field($USER->id, 'email', $values['email']);
        }
        redirect();
    }

    // TODO: Exception is the wrong type here!
    throw new Exception('Attempt by "' . $USER->get('username') . '@'
        . $USER->get('institution') . 'to change their password failed');
}

/**
 * Creates and displays the transient login page.
 *
 * This login page remembers all GET/POST data and passes it on. This way,
 * users can have their sessions time out, and then can log in again without
 * losing any of their data.
 *
 * As this function builds and validates a login form, it is possible that
 * calling this may validate a user to be logged in.
 *
 * @param Pieform $form If specified, just build this form to get the HTML
 *                      required. Otherwise, this function will build and
 *                      validate the form itself.
 * @access private
 */
function auth_draw_login_page($message=null, Pieform $form=null) {
    global $USER, $SESSION;
    if ($form != null) {
        $loginform = get_login_form_js($form->build());
    }
    else {
        require_once('pieforms/pieform.php');
        $loginform = get_login_form_js(pieform(auth_get_login_form()));
        /*
         * If $USER is set, the form was submitted even before being built.
         * This happens when a user's session times out and they resend post
         * data. The request should just continue if so.
         */
        if ($USER->is_logged_in()) {
            return;
        }

    }

    if ($message) {
        $SESSION->add_info_msg($message);
    }
    $smarty = smarty();
    $smarty->assign('login_form', $loginform);
    $smarty->assign('loginmessage', get_string('loginto', 'mahara', get_config('sitename')));
    $smarty->display('login.tpl');
    exit;
}

/**
 * Returns the definition of the login form.
 *
 * @return array   The login form definition array.
 * @access private
 */
function auth_get_login_form() {
    $institutions = get_records_menu('institution', '', '', 'name, displayname');
    $defaultinstitution = get_cookie('institution');
    if (!$defaultinstitution) {
        $defaultinstitution = 'mahara';
    }

    $elements = array(
        'login_username' => array(
            'type'        => 'text',
            'title'       => get_string('username') . ':',
            'description' => get_string('usernamedescription'),
            'rules' => array(
                'required'    => true
            )
        ),
        'login_password' => array(
            'type'        => 'password',
            'title'       => get_string('password') . ':',
            'description' => get_string('passworddescription'),
            'value'       => '',
            'rules' => array(
                'required'    => true
            )
        ),
        'submit' => array(
            'type'  => 'submit',
            'value' => get_string('login')
        ),
    );

    // The login page is completely transient, and it is smart because it
    // remembers the GET and POST data sent to it and resends that on
    // afterwards. 
    $action = '';
    if ($_GET) {
        if (isset($_GET['logout'])) {
            // You can log the user out on any particular page by appending
            // ?logout to the URL. In this case, we don't want the "action"
            // of the url to include that, or be blank, else the next time
            // the user logs in they will be logged out again.
            $action = hsc(substr($_SERVER['REQUEST_URI'], 0, strpos($_SERVER['REQUEST_URI'], '?')));
        } else {
            $action = '?';
            foreach ($_GET as $key => $value) {
                if ($key != 'logout') {
                    $action .= hsc($key) . '=' . hsc($value) . '&amp;';
                }
            }
            $action = substr($action, 0, -5);
        }
    }
    if ($_POST) {
        foreach ($_POST as $key => $value) {
            if (!isset($elements[$key]) && !isset($elements['login']['elements'][$key])) {
                $elements[$key] = array(
                    'type'  => 'hidden',
                    'value' => $value
                );
            }
        }
    }

    $form = array(
        'name'           => 'login',
        'method'         => 'post',
        'action'         => $action,
        'plugintype'     => 'auth',
        'pluginname'     => 'internal',
        'elements'       => $elements,
        'dieaftersubmit' => false,
        'iscancellable'  => false
    );

    return $form;
}

/**
 * Returns javascript to assist with the rendering of the login forms. The
 * javascript is used to detect whether cookies are enabled, and not show the
 * login form if they are not.
 *
 * @param string  $form A rendered login form
 * @return string The form with extra javascript added for cookie detection
 * @private
 */
function get_login_form_js($form) {
    $form = str_replace('/', '\/', str_replace("'", "\'", (str_replace(array("\n", "\t"), '', $form))));
    $strcookiesnotenabled    = json_encode(get_string('cookiesnotenabled'));
    $cookiename = get_config('cookieprefix') . 'ctest';
    return <<<EOF
<script type="text/javascript">
var loginbox = $('loginform_container');
document.cookie = "$cookiename=1";
if (document.cookie) {
    loginbox.innerHTML = '$form';
    document.cookie = '$cookiename=1;expires=1/1/1990 00:00:00';
}
else {
    replaceChildNodes(loginbox, P(null, $strcookiesnotenabled));
}
</script>
EOF;
}


/**
 * Class to build and cache instances of auth objects
 */
class AuthFactory {

    static $authcache = array();

    /**
     * Take an instanceid and create an auth object for that instance. 
     * 
     * @param  int      $id     The id of the auth instance
     * @return mixed            An intialised auth object or false, if the
     *                          instance doesn't exist (Should never happen)
     */
    public static function create($id) {

        if (isset(self::$authcache[$id]) && is_object(self::$authcache[$id])) {
            return self::$authcache[$id];
        }

        $authinstance = get_record('auth_instance', 'id', $id, null, null, null, null, 'authname');

        if (!empty($authinstance)) {
            $authclassname = 'Auth' . ucfirst($authinstance->authname);
            safe_require('auth', $authinstance->authname);
            self::$authcache[$id] = new $authclassname($id);
            return self::$authcache[$id];
        }

        return false;
    }
}

/**
 * Called when the login form is submitted. Validates the user and password, and
 * if they are valid, starts a new session for the user.
 *
 * @param object $form   The Pieform form object
 * @param array  $values The submitted values
 * @access private
 */
function login_submit(Pieform $form, $values) {
    global $SESSION, $USER;

    $username      = $values['login_username'];
    $password      = $values['login_password'];
    $authenticated = false;
    $oldlastlogin  = 0;

    try {
        //var_dump(array($username, $password, $institution, $_SESSION));
        $authenticated = $USER->login($username, $password);

        if (empty($authenticated)) {
            $SESSION->add_error_msg(get_string('loginfailed'));
        }

    }
    catch (AuthUnknownUserException $e) {
        try {
            // If the user doesn't exist, check for institutions that
            // want to create users automatically.
            $authinstances = get_records_sql_array('
                SELECT a.id, a.instancename, a.priority, a.authname, a.institution
                FROM {institution} i JOIN {auth_instance} a ON a.institution = i.name
                WHERE i.updateuserinfoonlogin = 1
                ORDER BY a.institution, a.priority, a.instancename', null);

            if ($authinstances == false) {
                throw new AuthUnknownUserException("\"$username\" is not known");
            }

            $USER->username = $username;

            foreach ($authinstances as $authinstance) {

                while (list(, $authinstance) = each($authinstances) && false == $authenticated) {
                    // TODO: Test this code with an auth plugin that provides a 
                    // get_user_info method
                    $auth = AuthFactory::create($authinstance->id);
                    if ($auth->authenticate_user_account($USER, $password)) {
                        $authenticated = true;
                    } else {
                        continue;
                    }