User Login Functions: Code Improvement
users:
    id -> int 11 auto pri
    fname -> varchar 50
    lname -> varchar 50
    phone -> int 45
    email -> varchar 100
    username -> varchar 50
    password -> varchar 100
    role -> varchar 5

public function login() {

        $this->form_validation->set_rules('username','Username', 'required|valid_email|trim|max_length[99]|xss_clean');
        $this->form_validation->set_rules('password','Password', 'required|trim|max_length[200]|xss_clean|callback__checkUsernamePassword');

        if($this->form_validation->run() === TRUE) {
        // set CLEAN data in the session.
            redirect('admin/dashboard');
        }

        $this->index();
    }

    function logout() {

        $this->session->sess_destroy();
        $this->index();

    }
     function _checkUsernamePassword() {
        // adding the _ makes the function 'private' so it can't be called from the URI.

            extract($_POST); // Gets data from form and creates vars

            $user = $this->login_model->check_login($username,$password);

            if(! $user){ // != If username or password are not correct
                $this->session->set_flashdata('login_error',TRUE); //does not add the non valid login to the session
                $this->form_validation->set_message('_checkUsernamePassword', 'Sorry %s is not correct.');
                return FALSE;

            } else {
                $this->session->set_userdata('logged_in',TRUE);
                $this->session->set_userdata('user_id',$user->id);
                $this->session->set_userdata('user_name',$user->first_name);
                $this->session->set_userdata('user_email',$user->email);
                return TRUE;

            }

function check_login($username,$password) {

    $query = $this->db->query("SELECT id, first_name, last_name, email, password FROM users WHERE email = ? and password = ?", array($username, md5($password))); // Result

    return ($query->num_rows() == 1) ? $query->row() : FALSE;

}