The authentication library.

Auth.php

<?php

class Auth
{
    private $hasher;
    private $session;

    function __construct()
    {   
        $this->hasher = new PasswordHash(8, false);
    }   

    function hash_password($password)
    {   
        return $this->hasher->HashPassword($password);
    }   

    function check_password($password, $hash)
    {   
        $result = false;
        if ($hash) {
            $result = $this->hasher->CheckPassword($password, $hash);
        }   
        return $result;
    }   

    function set_logged_in($user_id)
    {   
        $this->load_session();
        $this->session->set_userdata('user_id', $user_id);
    }   

    function is_logged_in()
    {   
        $this->load_session();
        return $this->session->userdata('user_id') > 0;
    }   

    function get_user_id()
    {   
        $this->load_session();
        return $this->session->userdata('user_id');
    }   

    function set_logged_out()
    {   
        $this->load_session();
        $this->session->unset_userdata('user_id');
    }   

    private function load_session()
    {   
        if (!$this->session) {
            $ci = get_instance();
            $this->session = $ci->session;
        }   
    }   
}