public function delete_key()
 {
     if (Pki::exists(array('id' => $_GET['id'], 'user_id' => $this->user->id))) {
         Pki::delete($_GET['id']);
         $this->redirect_to(url_for('UserController', 'edit'));
     } else {
         $this->redirect_to(url_for('UserController', 'edit'));
     }
     $this->has_rendered = true;
 }