如何登录两个不同的codeigniter项目

Question

I have two different CodeIgniter project first is on a root domain and another one is one subdomain.

I try to use the existing login function of both the projects, I put my multi-login code in subdomain its work fine

Checking whether it's available or not in a subdomain or if not present check the root domain database

after submitting the form it comes here in checkUser()

 function checkUser(){  

             $username = $this->input->post('username');  
             $password = $this->input->post('password');

             $this->load->model('CheckUserModel');
             $data = $this->CheckUserModel->checkUser($username,$password);
  if($data['user']['instance']=="sub-domain"){
            print_r("Inside Subdomain instance");


        //Model Function
        $this->load->model('login_model');

        if ($this->login_model->can_login_valid($username,$password)) {

            $data = $this->login_model->can_login($username,$password);


               redirect(base_url());
            //redirect(base_url().'user/SigninController/enter');
        }else {

            $this->session->set_flashdata('error','Invalid Username and Password');
            redirect(base_url().'user/CheckUserContoller/');
        }


      }else if($data['user']['instance']=="root-domain"){
            print_r("Inside root-doamin instance");


        //Model Function
        $this->load->model('login_model');


        if ($this->login_model->can_login_valid2($username,$password)) {

            $data = $this->login_model->can_login2($username,$password);


              //load the Curl library
              $this->load->library('curl');       

              //Request using POST Method
              $url = 'https://root-domain.online/user/SigninController/';     
              $postData= array(

                           "user_email" => $username,
                           "user_password" => $password,
                           'redirect_to' => $url,
                           'testcookie' => '1'
                        );


            curl_setopt_array($ch, array(
                CURLOPT_URL => 'https://root-domain.online/user/SigninController/login_validation',
                CURLOPT_RETURNTRANSFER => true,
                CURLOPT_POST => true,
                CURLOPT_POSTFIELDS => $postData,
                CURLOPT_FOLLOWLOCATION => true
            ));

            $output = curl_exec($ch);
            echo $output;

            //redirect(base_url().'user/SigninController/enter');
        }else {

            $this->session->set_flashdata('error','Invalid Username and Password');
            redirect(base_url().'user/CheckUserContoller/');
        }
         }
}

it works fine in a subdomain and logged in me

but the problem is that when I try to login to root domain it shows the login page