Well it's not really a problem but I check if the user exist and log them in and redirect to site/members_area, but I don't want to send the user to a specific page but i want to reload the current controller. So if I login in index/home I would like to be redirected at index/home, how should I proceed?

in regular php I would put in the action to redirect to current page

<?php echo $_SERVER['PHP_SELF']; ?>

This is the code in the framework

function validate_credentials()
    {       
        $this->load->model('membership_model');
        $query = $this->membership_model->validate();

        if($query) // if the user's credentials validated...
        {
            $data = array(
                'username' => $this->input->post('username'),
                'is_logged_in' => true
            );
            $this->session->set_userdata($data);
            redirect('site/members_area'); //<-- this line here should be dynamic
        }
        else // incorrect username or password
        {
            $this->index();
        }
    }