Fungsi dasar :
function do_login($username)
	{
		$CI =& get_instance();
		$CI->db->select('tb_user.*, tb_level.*');
		$CI->db->from('tb_user');
		$CI->db->join('tb_level','tb_user.user_level = tb_level.id_level','left');
		$CI->db->where('tb_user.user_username',$username);

		$result = $CI->db->get();
		if($result->num_rows() == 0)
		{
			return false;
		}
		else
		{
				$userdata = $result->row();
				$session_data = array(
					'level'			=> $userdata->user_level,
					'username'		=> $userdata->user_username,
					'namauser'		=> $userdata->user_nama,

				);
				$CI->session->set_userdata($session_data);

				return true;
		}
	}

Penggunaan :
	function is_logged_in()
	{
		$CI =& get_instance();

		if($CI->session->userdata('username') == '')
		{
			return false;
		}
		else
		{
			return true;
		}

	}

	function __construct()
	{
		parent::__construct();
		$this->load->library(array('template', 'form_validation', 'pagination'));
		if(!$this->auth->is_logged_in())
		{
			redirect('web');
		}

	}

Table :
CREATE TABLE IF NOT EXISTS `tb_user` (
  `id_user` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00' ON UPDATE CURRENT_TIMESTAMP,
  `user_username` varchar(100) DEFAULT NULL,
  `user_nama` varchar(100) DEFAULT NULL,
  `user_level` int DEFAULT NULL,
  `user_foto` varchar(250) DEFAULT NULL,
  PRIMARY KEY (`id_user`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

CREATE TABLE IF NOT EXISTS `tb_level` (
  `id_level` int NOT NULL,
  `nama_level` varchar(50) NOT NULL,
  PRIMARY KEY (`id_level`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

CREATE TABLE IF NOT EXISTS `kategori_menu` (
  `id_kategori` varchar(50) NOT NULL,
  `allowed` varchar(20) DEFAULT NULL,
  `sub` varchar(50) DEFAULT NULL,
  `icon` varchar(20) DEFAULT NULL,
  `alamat` varchar(50) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;