Codeigniter Auth system based on device - php

Question

I am kind of newbie around here so hope i am doing fine what am i doing.
I started working with Codeignter recently and trying to build a secured login to restrict access from three devices only.
On login
I am trying to add a never-expiring "device_id" cookie upon successful authentication. That cookie would be a a unique string and store it into database
And if the user has aleady three devices stored to be rejected.
If the user has available devices slots, this to be recorded and added to its stack.
Basicly i want to allow access if the user has avail slots or the cookie arleady exists.
Have any ideea where should i start or there is a Codeigniter library ?
The code from my control that alows and valides login is:
function login()
{
if ($this->session->userdata('logged_in'))
{
$logged_in_user = $this->session->userdata('logged_in');
if ($logged_in_user['is_admin'])
{
redirect('admin');
}
else
{
redirect(base_url());
}
}
// set form validation rules
$this->form_validation->set_error_delimiters($this->config->item('error_delimeter_left'), $this->config->item('error_delimeter_right'));
$this->form_validation->set_rules('username', lang('users input username_email'), 'required|trim');
$this->form_validation->set_rules('password', lang('users input password'), 'required|trim|callback__check_login');
if ($this->form_validation->run() == TRUE)
{
if ($this->session->userdata('redirect'))
{
$redirect = $this->session->userdata('redirect');
$this->session->unset_userdata('redirect');
redirect($redirect);
}
else
{
$logged_in_user = $this->session->userdata('logged_in');
if ($logged_in_user['is_admin'])
{
redirect('admin');
}
else
{
redirect(base_url());
}
}
}
// setup page header data
$this->add_css_theme( 'login.css' );
$this->set_title( lang('users title login') );
$data = $this->includes;
// load views
$data['content'] = $this->load->view('user/login', NULL, TRUE);
$this->load->view($this->template, $data);
}

Answer 1

it's not a good idea to write your system ....you can not secure your auth system from session hijacking (when session_id not change in long period) , dos attack , ddos attack , etc very easliy .... it's better to use early written system like auth_ion ....
you can find authentication library for code igniter in :
https://github.com/bcit-ci/CodeIgniter/wiki/Contributions#libraries
i preffer ion_auth in that list ...