eZ Platform Service to login user programatically

LoginService.php

<?php

namespace Vendor\MyLoginBundle\Services;

use Symfony\Component\HttpFoundation\RequestStack,  
    Symfony\Component\HttpFoundation\Response,
    Symfony\Component\HttpFoundation\Cookie;

class LoginService
{
    private $requestStack;

    public function __construct(RequestStack $requestStack)
    {
        $this->requestStack = $requestStack;
    }

    public function setLoggedInUser($userId)
    {
        $session = $this->requestStack->getCurrentRequest()->getSession();
        $session->set('eZUserLoggedInID', $userId);
        $response = new Response();
        $response->headers->setCookie(new Cookie('is_logged_in', 'true'));
    }
}

You should inject the requestStack in the service configuration:

services:
    myvendor.login.service:
        class: Vendor\MyLoginBundle\Services\LoginService
        arguments:
            - @request_stack