Can't log in user with Rest service
Finally, it works :D, I'll just put this answer here to help how still don't know how to login user via my custom Web Services API, i had to manage the cookies from the frontend, I use symfony, after sending a POST request to /{endpoint}/user/login, and receive the response that will look like this:

{
    "sessid": "ZkJ26dMEQQ-K3VkE9zv2Cni2lWergSOOnPlF3jkiF-Q",
    "session_name": "SESS948facaca231cedd9a2a526239dcb6dc",
    "token": "icfD3CNT4r4QAlEGiYmqzez0MVmsPbAowVR8HtfaD4Y",
    "user": {
        "uid": "1",
        "name": "admin",
        "mail": "contact@headless.com",
        "theme": "",
        "signature": "",
        "signature_format": null,
        "created": "1459037019",
        "access": "1459439836",
        "login": 1459440402,
        "status": "1",
        "timezone": "Europe/Paris",
        "language": "",
        "picture": "0",
        "init": "contact@headless.com",
        "data": false,
        "roles": {
            "2": "authenticated user"
        }
    }
}


i create a cookie with (any name) and the value will be "session_name=sessid", don't forget the "=".
and finally to see if the user is logged in, you need the token and the cookie that you created, send a POST request to {endpoint}/system/connect WITH this HEADERS:

X-CSRF-Token: token from the login response
Cookie: SESS948facaca231cedd9a2a526239dcb6dc=ZkJ26dMEQQ-K3VkE9zv2Cni2lWergSOOnPlF3jkiF-Q (session_name=sessid)


and voila :D, you get a response like this:

{
    "sessid": "ZkJ26dMEQQ-K3VkE9zv2Cni2lWergSOOnPlF3jkiF-Q",
    "session_name": "SESS948facaca231cedd9a2a526239dcb6dc",
    "user": {
        "uid": "1",
        "name": "admin",
        "mail": "contact@headless.com",
        "theme": "",
        "signature": "",
        "signature_format": null,
        "created": "1459037019",
        "access": "1459440402",
        "login": "1459440402",
        "status": "1",
        "timezone": "Europe/Paris",
        "language": "",
        "picture": "0",
        "init": "contact@headless.com",
        "data": false,
        "sid": "ZkJ26dMEQQ-K3VkE9zv2Cni2lWergSOOnPlF3jkiF-Q",
        "ssid": "",
        "hostname": "127.0.0.1",
        "timestamp": "1459440402",
        "cache": "0",
        "session": "",
        "roles": {
            "2": "authenticated user"
        }
    }
}


i hope my answer help any one how is looking for how to login users via Drupal Services.