How to create session for user which is not an admin user

// ADMIN

$user_id = 1;
require_once (ABSPATH . ‘wp-includes/pluggable.php’);

if (!is_admin())
{

// DEMO USER

$user_id = 6;
}

if ($current_user_id != $user_id)
{
$user = get_user_by(‘id’, $user_id);
if ($user)
{
wp_set_current_user($user_id, $user->user_login);

    // wp_set_auth_cookie($user_id);

    if (wp_validate_auth_cookie('', 'logged_in') != $user_id)
        {
        wp_set_auth_cookie($user_id);
        }

    // do_action('wp_login', $user->user_login);

    }
}