<?php defined("SYSPATH") or die("No direct script access.");
/**
 * Gallery - a web based photo album viewer and editor
 * Copyright (C) 2000-2010 Bharat Mediratta
 *
 * 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 2 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, write to the Free Software
 * Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, MA  02110-1301, USA.
 */
/**
 * API for Gallery Access control.
 *
 * Permissions are hierarchical, and apply only to groups and albums.  They cascade down from the
 * top of the Gallery to the bottom, so if you set a permission in the root album, that permission
 * applies for any sub-album unless the sub-album overrides it.  Likewise, any permission applied
 * to an album applies to any photos inside the album.  Overrides can be applied at any level of
 * the hierarchy for any permission other than View permissions.
 *
 * View permissions are an exceptional case.  In the case of viewability, we want to ensure that
 * if an album's parent is inaccessible, then this album must be inaccessible also.  So while view
 * permissions cascade downwards and you're free to set the ALLOW permission on any album, that
 * ALLOW permission will be ignored unless all that album's parents are marked ALLOW also.
 *
 * Implementatation Notes:
 *
 * Notes refer to this example album hierarchy:
 *      A1
 *     /  \
 *   A2   A3
 *       /  \
 *      A4  A5
 *
 * o We have the concept of "intents".  A user can specify that he intends for A3 to be
 *   inaccessible (ie: a DENY on the "view" permission to the EVERYBODY group).  Once A3 is
 *   inaccessible, A5 can never be displayed to that group.  If A1 is made inaccessible, then the
 *   entire tree is hidden.  If subsequently A1 is made accessible, then the whole tree is
 *   available again *except* A3 and below since the user's "intent" for A3 is maintained.
 *
 * o Intents are specified as <group_id, perm, item_id> tuples.  It would be inefficient to check
 *   these tuples every time we want to do a lookup, so we use these intents to create an entire
 *   table of permissions for easy lookup in the Access_Cache_Model.  There's a 1:1 mapping
 *   between Item_Model and Access_Cache_Model entries.
 *
 * o For efficiency, we create columns in Access_Intent_Model and Access_Cache_Model for each of
 *   the possible Group_Model and Permission_Model combinations.  This may lead to performance
 *   issues for very large Gallery installs, but for small to medium sized ones (5-10 groups, 5-10
 *   permissions) it's especially efficient because there's a single field value for each
 *   group/permission/item combination.
 *
 * o For efficiency, we store the cache columns for view permissions directly in the Item_Model.
 *   This means that we can filter items by group/permission combination without doing any table
 *   joins making for an especially efficient permission check at the expense of having to
 *   maintain extra columns for each item.
 *
 * o If at any time the Access_Cache_Model becomes invalid, we can rebuild the entire table from
 *   the Access_Intent_Model
 */
class access_Core {
  const DENY      = "0";
  const ALLOW     = "1";
  const INHERIT   = null; // access_intent
  const UNKNOWN   = null; // cache (access_cache, items)

  /**
   * Does the active user have this permission on this item?
   *
   * @param  string     $perm_name
   * @param  Item_Model $item
   * @return boolean
   */
  static function can($perm_name, $item) {
    return access::user_can(identity::active_user(), $perm_name, $item);
  }

  /**
   * Does the user have this permission on this item?
   *
   * @param  User_Model $user
   * @param  string     $perm_name
   * @param  Item_Model $item
   * @return boolean
   */
  static function user_can($user, $perm_name, $item) {
    if (!$item->loaded()) {
      return false;
    }

    if ($user->admin) {
      return true;
    }

    /*
      We do this for cache reasons - if you check n photos in an album, it makes more sense
      to check the album permissions once and let the cache deal with that, rather than check
      every item individually and generate cache misses.
    */
    $id = ($item->type == 'album') ? $item->id : $item->parent_id;
    $resource = $perm_name == "view" ?
      $item : model_cache::get("access_cache", $id, "item_id");
      
    foreach ($user->groups() as $group) {
      if ($resource->__get("{$perm_name}_{$group->id}") === access::ALLOW) {
        return true;
      }
    }
    return false;
  }

  /**
   * If the active user does not have this permission, failed with an access::forbidden().
   *
   * @param  string     $perm_name
   * @param  Item_Model $item
   * @return boolean
   */
  static function required($perm_name, $item) {
    if (!access::can($perm_name, $item)) {
      if ($perm_name == "view") {
        // Treat as if the item didn't exist, don't leak any information.
        throw new Kohana_404_Exception();
      } else {
        access::forbidden();
      }
    }
  }

  /**
   * Does this group have this permission on this item?
   *
   * @param  Group_Model $group
   * @param  string      $perm_name
   * @param  Item_Model  $item
   * @return boolean
   */
  static function group_can($group, $perm_name, $item) {
    /*
      We do this for cache reasons - if you check n photos in an album, it makes more sense
      to check the album permissions once and let the cache deal with that, rather than check
      every item individually and generate cache misses.
    */
    $id = ($item->type == 'album') ? $item->id : $item->parent_id;
    $resource = $perm_name == "view" ?
      $item : model_cache::get("access_cache", $id, "item_id");
      
    return $resource->__get("{$perm_name}_{$group->id}") === access::ALLOW;
  }

  /**
   * Return this group's intent for this permission on this item.
   *
   * @param  Group_Model $group
   * @param  string      $perm_name
   * @param  Item_Model  $item
   * @return boolean     access::ALLOW, access::DENY or access::INHERIT (null) for no intent
   */
  static function group_intent($group, $perm_name, $item) {
    $intent = model_cache::get("access_intent", $item->id, "item_id");
    return $intent->__get("{$perm_name}_{$group->id}");
  }

  /**
   * Is the permission on this item locked by a parent?  If so return the nearest parent that
   * locks it.
   *
   * @param  Group_Model $group
   * @param  string      $perm_name
   * @param  Item_Model  $item
   * @return ORM_Model   item that locks this one
   */
  static function locked_by($group, $perm_name, $item) {
    if ($perm_name != "view") {
      return null;
    }

    // For view permissions, if any parent is access::DENY, then those parents lock this one.
    // Return
    $lock = ORM::factory("item")
      ->where("left_ptr", "<=", $item->left_ptr)
      ->where("right_ptr", ">=", $item->right_ptr)
      ->where("items.id", "<>", $item->id)
      ->join("access_intents", "items.id", "access_intents.item_id")
      ->where("access_intents.view_$group->id", "=", access::DENY)
      ->order_by("level", "DESC")
      ->limit(1)
      ->find();

    if ($lock->loaded()) {
      return $lock;
    } else {
      return null;
    }
  }

  /**
   * Terminate immediately with an HTTP 403 Forbidden response.
   */
  static function forbidden() {
    throw new Kohana_Exception("@todo FORBIDDEN", null, 403);
  }

  /**
   * Internal method to set a permission
   *
   * @param  Group_Model $group
   * @param  string      $perm_name
   * @param  Item_Model  $item
   * @param  boolean     $value
   */
  private static function _set(Group_Definition $group, $perm_name, $album, $value) {
    if (!($group instanceof Group_Definition)) {
      throw new Exception("@todo PERMISSIONS_ONLY_WORK_ON_GROUPS");
    }
    if (!$album->loaded()) {
      throw new Exception("@todo INVALID_ALBUM $album->id");
    }
    if (!$album->is_album()) {
      throw new Exception("@todo INVALID_ALBUM_TYPE not an album");
    }
    $access = model_cache::get("access_intent", $album->id, "item_id");
    $access->__set("{$perm_name}_{$group->id}", $value);
    $access->save();

    if ($perm_name == "view") {
      self::_update_access_view_cache($group, $album);
    } else {
      self::_update_access_non_view_cache($group, $perm_name, $album);
    }

    access::update_htaccess_files($album, $group, $perm_name, $value);
    model_cache::clear();
  }

  /**
   * Allow a group to have a permission on an item.
   *
   * @param  Group_Model $group
   * @param  string  $perm_name
   * @param  Item_Model $item
   */
  static function allow($group, $perm_name, $item) {
    self::_set($group, $perm_name, $item, self::ALLOW);
  }

  /**
   * Deny a group the given permission on an item.
   *
   * @param  Group_Model $group
   * @param  string  $perm_name
   * @param  Item_Model $item
   */
  static function deny($group, $perm_name, $item) {
    self::_set($group, $perm_name, $item, self::DENY);
  }

  /**
   * Unset the given permission for this item and use inherited values
   *
   * @param  Group_Model $group
   * @param  string  $perm_name
   * @param  Item_Model $item
   */
  static function reset($group, $perm_name, $item) {
    if ($item->id == 1) {
      throw new Exception("@todo CANT_RESET_ROOT_PERMISSION");
    }
    self::_set($group, $perm_name, $item, self::INHERIT);
  }

  /**
   * Recalculate the permissions for an album's hierarchy.
   */
  static function recalculate_album_permissions($album) {
    foreach (self::_get_all_groups() as $group) {
      foreach (ORM::factory("permission")->find_all() as $perm) {
        if ($perm->name == "view") {
          self::_update_access_view_cache($group, $album);
        } else {
          self::_update_access_non_view_cache($group, $perm->name, $album);
        }
      }
    }
    model_cache::clear();
  }

  /**
   * Recalculate the permissions for a single photo.
   */
  static function recalculate_photo_permissions($photo) {
    $parent = $photo->parent();
    $parent_access_cache = ORM::factory("access_cache")->where("item_id", "=", $parent->id)->find();
    $photo_access_cache = ORM::factory("access_cache")->where("item_id", "=", $photo->id)->find();
    foreach (self::_get_all_groups() as $group) {
      foreach (ORM::factory("permission")->find_all() as $perm) {
        $field = "{$perm->name}_{$group->id}";
        if ($perm->name == "view") {
          $photo->$field = $parent->$field;
        } else {
          $photo_access_cache->$field = $parent_access_cache->$field;
        }
      }
    }
    $photo_access_cache->save();
    $photo->save();
    model_cache::clear();
  }

  /**
   * Register a permission so that modules can use it.
   *
   * @param  string $name           The internal name for for this permission
   * @param  string $display_name   The internationalized version of the displayable name
   * @return void
  */
  static function register_permission($name, $display_name) {
    $permission = ORM::factory("permission", $name);
    if ($permission->loaded()) {
      throw new Exception("@todo PERMISSION_ALREADY_EXISTS $name");
    }
    $permission->name = $name;
    $permission->display_name = $display_name;
    $permission->save();

    foreach (self::_get_all_groups() as $group) {
      self::_add_columns($name, $group);
    }
  }

  /**
   * Delete a permission.
   *
   * @param  string $perm_name
   * @return void
   */
  static function delete_permission($name) {
    foreach (self::_get_all_groups() as $group) {
      self::_drop_columns($name, $group);
    }
    $permission = ORM::factory("permission")->where("name", "=", $name)->find();
    if ($permission->loaded()) {
      $permission->delete();
    }
  }

  /**
   * Add the appropriate columns for a new group
   *
   * @param Group_Model $group
   * @return void
   */
  static function add_group($group) {
    foreach (ORM::factory("permission")->find_all() as $perm) {
      self::_add_columns($perm->name, $group);
    }
  }

  /**
   * Remove a group's permission columns (usually when it's deleted)
   *
   * @param Group_Model $group
   * @return void
   */
  static function delete_group($group) {
    foreach (ORM::factory("permission")->find_all() as $perm) {
      self::_drop_columns($perm->name, $group);
    }
  }

  /**
   * Add new access rows when a new item is added.
   *
   * @param Item_Model $item
   * @return void
   */
  static function add_item($item) {
    $access_intent = ORM::factory("access_intent", $item->id);
    if ($access_intent->loaded()) {
      throw new Exception("@todo ITEM_ALREADY_ADDED $item->id");
    }
    $access_intent = ORM::factory("access_intent");
    $access_intent->item_id = $item->id;
    $access_intent->save();

    // Create a new access cache entry and copy the parents values.
    $access_cache = ORM::factory("access_cache");
    $access_cache->item_id = $item->id;
    if ($item->id != 1) {
      $parent_access_cache =
        ORM::factory("access_cache")->where("item_id", "=", $item->parent()->id)->find();
      foreach (self::_get_all_groups() as $group) {
        foreach (ORM::factory("permission")->find_all() as $perm) {
          $field = "{$perm->name}_{$group->id}";
          if ($perm->name == "view") {
            $item->$field = $item->parent()->$field;
          } else {
            $access_cache->$field = $parent_access_cache->$field;
          }
        }
      }
    }
    $item->save();
    $access_cache->save();
  }

  /**
   * Delete appropriate access rows when an item is deleted.
   *
   * @param Item_Model $item
   * @return void
   */
  static function delete_item($item) {
    ORM::factory("access_intent")->where("item_id", "=", $item->id)->find()->delete();
    ORM::factory("access_cache")->where("item_id", "=", $item->id)->find()->delete();
  }

  /**
   * Verify our Cross Site Request Forgery token is valid, else throw an exception.
   */
  static function verify_csrf() {
    $input = Input::instance();
    if ($input->post("csrf", $input->get("csrf", null)) !== Session::instance()->get("csrf")) {
      access::forbidden();
    }
  }

  /**
   * Get the Cross Site Request Forgery token for this session.
   * @return string
   */
  static function csrf_token() {
    $session = Session::instance();
    $csrf = $session->get("csrf");
    if (empty($csrf)) {
      $csrf = random::hash();
      $session->set("csrf", $csrf);
    }
    return $csrf;
  }

  /**
   * Generate an <input> element containing the Cross Site Request Forgery token for this session.
   * @return string
   */
  static function csrf_form_field() {
    return "<input type=\"hidden\" name=\"csrf\" value=\"" . access::csrf_token() . "\"/>";
  }

  /**
   * Internal method to get all available groups.
   *
   * @return ORM_Iterator
   */
  private static function _get_all_groups() {
    // When we build the gallery package, it's possible that there is no identity provider
    // installed yet.  This is ok at packaging time, so work around it.
   if (module::is_active(module::get_var("gallery", "identity_provider", "user"))) {
      return identity::groups();
    } else {
      return array();
    }
  }

  /**
   * Internal method to  remove Permission/Group columns
   *
   * @param  Group_Model $group
   * @param  string      $perm_name
   * @return void
   */
  private static function _drop_columns($perm_name, $group) {
    $field = "{$perm_name}_{$group->id}";
    $cache_table = $perm_name == "view" ? "items" : "access_caches";
    Database::instance()->query("ALTER TABLE {{$cache_table}} DROP `$field`");
    Database::instance()->query("ALTER TABLE {access_intents} DROP `$field`");
    model_cache::clear();
    ORM::factory("access_intent")->clear_cache();
  }

  /**
   * Internal method to add Permission/Group columns
   *
   * @param  Group_Model $group
   * @param  string  $perm_name
   * @return void
   */
  private static function _add_columns($perm_name, $group) {
    $field = "{$perm_name}_{$group->id}";
    $cache_table = $perm_name == "view" ? "items" : "access_caches";
    $not_null = $cache_table == "items" ? "" : "NOT NULL";
    Database::instance()->query(
      "ALTER TABLE {{$cache_table}} ADD `$field` BINARY $not_null DEFAULT FALSE");
    Database::instance()->query(
      "ALTER TABLE {access_intents} ADD `$field` BINARY DEFAULT NULL");
    db::build()
      ->update("access_intents")
      ->set($field, access::DENY)
      ->where("item_id", "=", 1)
      ->execute();
    model_cache::clear();
    ORM::factory("access_intent")->clear_cache();
  }

  /**
   * Update the Access_Cache model based on information from the Access_Intent model for view
   * permissions only.
   *
   * @todo: use database locking
   *
   * @param  Group_Model $group
   * @param  Item_Model $item
   * @return void
   */
  private static function _update_access_view_cache($group, $item) {
    $access = ORM::factory("access_intent")->where("item_id", "=", $item->id)->find();
    $field = "view_{$group->id}";

    // With view permissions, deny values in the parent can override allow values in the child,
    // so start from the bottom of the tree and work upwards overlaying negative on top of
    // positive.
    //
    // If the item's intent is ALLOW or DEFAULT, it's possible that some ancestor has specified
    // DENY and this ALLOW cannot be obeyed.  So in that case, back up the tree and find any
    // non-DEFAULT and non-ALLOW parent and propagate from there.  If we can't find a matching
    // item, then its safe to propagate from here.
    if ($access->$field !== access::DENY) {
      $tmp_item = ORM::factory("item")
        ->where("left_ptr", "<", $item->left_ptr)
        ->where("right_ptr", ">", $item->right_ptr)
        ->join("access_intents", "access_intents.item_id", "items.id")
        ->where("access_intents.$field", "=", access::DENY)
        ->order_by("left_ptr", "DESC")
        ->limit(1)
        ->find();
      if ($tmp_item->loaded()) {
        $item = $tmp_item;
      }
    }

    // We will have a problem if we're trying to change a DENY to an ALLOW because the
    // access_caches table will already contain DENY values and we won't be able to overwrite
    // them according the rule above.  So mark every permission below this level as UNKNOWN so
    // that we can tell which permissions have been changed, and which ones need to be updated.
    db::build()
      ->update("items")
      ->set($field, access::UNKNOWN)
      ->where("left_ptr", ">=", $item->left_ptr)
      ->where("right_ptr", "<=", $item->right_ptr)
      ->execute();

    $query = ORM::factory("access_intent")
      ->select(array("access_intents.$field", "items.left_ptr", "items.right_ptr", "items.id"))
      ->join("items", "items.id", "access_intents.item_id")
      ->where("left_ptr", ">=", $item->left_ptr)
      ->where("right_ptr", "<=", $item->right_ptr)
      ->where("type", "=", "album")
      ->where("access_intents.$field", "IS NOT", access::INHERIT)
      ->order_by("level", "DESC")
      ->find_all();
    foreach ($query as $row) {
      if ($row->$field == access::ALLOW) {
        // Propagate ALLOW for any row that is still UNKNOWN.
        db::build()
          ->update("items")
          ->set($field, $row->$field)
          ->where($field, "IS", access::UNKNOWN) // UNKNOWN is NULL so we have to use IS
          ->where("left_ptr", ">=", $row->left_ptr)
          ->where("right_ptr", "<=", $row->right_ptr)
          ->execute();
      } else if ($row->$field == access::DENY) {
        // DENY overwrites everything below it
        db::build()
          ->update("items")
          ->set($field, $row->$field)
          ->where("left_ptr", ">=", $row->left_ptr)
          ->where("right_ptr", "<=", $row->right_ptr)
          ->execute();
      }
    }

    // Finally, if our intent is DEFAULT at this point it means that we were unable to find a
    // DENY parent in the hierarchy to propagate from.  So we'll still have a UNKNOWN values in
    // the hierarchy, and all of those are safe to change to ALLOW.
    db::build()
      ->update("items")
      ->set($field, access::ALLOW)
      ->where($field, "IS", access::UNKNOWN) // UNKNOWN is NULL so we have to use IS
      ->where("left_ptr", ">=", $item->left_ptr)
      ->where("right_ptr", "<=", $item->right_ptr)
      ->execute();
  }

  /**
   * Update the Access_Cache model based on information from the Access_Intent model for non-view
   * permissions.
   *
   * @todo: use database locking
   *
   * @param  Group_Model $group
   * @param  string  $perm_name
   * @param  Item_Model $item
   * @return void
   */
  private static function _update_access_non_view_cache($group, $perm_name, $item) {
    $access = ORM::factory("access_intent")->where("item_id", "=", $item->id)->find();

    $field = "{$perm_name}_{$group->id}";

    // If the item's intent is DEFAULT, then we need to back up the chain to find the nearest
    // parent with an intent and propagate from there.
    //
    // @todo To optimize this, we wouldn't need to propagate from the parent, we could just
    //       propagate from here with the parent's intent.
    if ($access->$field === access::INHERIT) {
      $tmp_item = ORM::factory("item")
        ->join("access_intents", "items.id", "access_intents.item_id")
        ->where("left_ptr", "<", $item->left_ptr)
        ->where("right_ptr", ">", $item->right_ptr)
        ->where($field, "IS NOT", access::UNKNOWN) // UNKNOWN is NULL so we have to use IS NOT
        ->order_by("left_ptr", "DESC")
        ->limit(1)
        ->find();
      if ($tmp_item->loaded()) {
        $item = $tmp_item;
      }
    }

    // With non-view permissions, each level can override any permissions that came above it
    // so start at the top and work downwards, overlaying permissions as we go.
    $query = ORM::factory("access_intent")
      ->select(array("access_intents.$field", "items.left_ptr", "items.right_ptr"))
      ->join("items", "items.id", "access_intents.item_id")
      ->where("left_ptr", ">=", $item->left_ptr)
      ->where("right_ptr", "<=", $item->right_ptr)
      ->where($field, "IS NOT", access::INHERIT)
      ->order_by("level", "ASC")
      ->find_all();
    foreach ($query as $row) {
      $value = ($row->$field === access::ALLOW) ? true : false;
      db::build()
        ->update("access_caches")
        ->set($field, $value)
        ->where("item_id", "IN",
                db::build()
                ->select("id")
                ->from("items")
                ->where("left_ptr", ">=", $row->left_ptr)
                ->where("right_ptr", "<=", $row->right_ptr))
        ->execute();
    }
  }

  /**
   * Rebuild the .htaccess files that prevent direct access to albums, resizes and thumbnails.  We
   * call this internally any time we change the view or view_full permissions for guest users.
   * This function is only public because we use it in maintenance tasks.
   *
   * @param  Item_Model   the album
   * @param  Group_Model  the group whose permission is changing
   * @param  string       the permission name
   * @param  string       the new permission value (eg access::DENY)
   */
  static function update_htaccess_files($album, $group, $perm_name, $value) {
    if ($group->id != identity::everybody()->id ||
        !($perm_name == "view" || $perm_name == "view_full")) {
      return;
    }

    $dirs = array($album->file_path());
    if ($perm_name == "view") {
      $dirs[] = dirname($album->resize_path());
      $dirs[] = dirname($album->thumb_path());
    }

    $base_url = url::base(true);
    $sep = "?";
    if (strpos($base_url, "?") !== false) {
      $sep = "&";
    }
    $base_url .= $sep . "kohana_uri=/file_proxy";
    // Replace "/index.php/?kohana..." with "/index.php?koahan..."
    // Doesn't apply to "/?kohana..." or "/foo/?kohana..."
    // Can't check for "index.php" since the file might be renamed, and
    // there might be more Apache aliases / rewrites at work.
    $url_path = parse_url($base_url, PHP_URL_PATH);
    // Does the URL path have a file component?
    if (preg_match("#[^/]+\.php#i", $url_path)) {
      $base_url = str_replace("/?", "?", $base_url);
    }

    foreach ($dirs as $dir) {
      if ($value === access::DENY) {
        $fp = fopen("$dir/.htaccess", "w+");
        fwrite($fp, "<IfModule mod_rewrite.c>\n");
        fwrite($fp, "  RewriteEngine On\n");
        fwrite($fp, "  RewriteRule (.*) $base_url/\$1 [L]\n");
        fwrite($fp, "</IfModule>\n");
        fwrite($fp, "<IfModule !mod_rewrite.c>\n");
        fwrite($fp, "  Order Deny,Allow\n");
        fwrite($fp, "  Deny from All\n");
        fwrite($fp, "</IfModule>\n");
        fclose($fp);
      } else {
        @unlink($dir . "/.htaccess");
      }
    }
  }

  static function private_key() {
    return module::get_var("gallery", "private_key");
  }

  /**
   * Verify that our htaccess based permission system actually works.  Create a temporary
   * directory containing an .htaccess file that uses mod_rewrite to redirect /verify to
   * /success.  Then request that url.  If we retrieve it successfully, then our redirects are
   * working and our permission system works.
   */
  static function htaccess_works() {
    $success_url = url::file("var/security_test/success");

    @mkdir(VARPATH . "security_test");
    try {
      if ($fp = @fopen(VARPATH . "security_test/.htaccess", "w+")) {
        fwrite($fp, "Options +FollowSymLinks\n");
        fwrite($fp, "RewriteEngine On\n");
        fwrite($fp, "RewriteRule verify $success_url [L]\n");
        fclose($fp);
      }

      if ($fp = @fopen(VARPATH . "security_test/success", "w+")) {
        fwrite($fp, "success");
        fclose($fp);
      }

      // Proxy our authorization headers so that if the entire Gallery is covered by Basic Auth
      // this callback will still work.
      $headers = array();
      if (function_exists("apache_request_headers")) {
        $arh = apache_request_headers();
        if (!empty($arh["Authorization"])) {
          $headers["Authorization"] = $arh["Authorization"];
        }
      }
      list ($status, $headers, $body) =
        remote::do_request(url::abs_file("var/security_test/verify"), "GET", $headers);
      $works = ($status == "HTTP/1.1 200 OK") && ($body == "success");
    } catch (Exception $e) {
      @dir::unlink(VARPATH . "security_test");
      throw $e;
    }
    @dir::unlink(VARPATH . "security_test");

    return $works;
  }
}