function onLogin($user) {
    $token = GenerateRandomToken(); // generate a token, should be 128 - 256 bit
    storeTokenForUser($user, $token);
    $cookie = $user . ':' . $token;
    $mac = hash_hmac('sha256', $cookie, SECRET_KEY);
    $cookie .= ':' . $mac;
    setcookie('rememberme', $cookie);
}

function rememberMe() {
    $cookie = isset($_COOKIE['rememberme']) ? $_COOKIE['rememberme'] : '';
    if ($cookie) {
        list ($user, $token, $mac) = explode(':', $cookie);
        if (!hash_equals(hash_hmac('sha256', $user . ':' . $token, SECRET_KEY), $mac)) {
            return false;
        }
        $usertoken = fetchTokenByUserName($user);
        if (hash_equals($usertoken, $token)) {
            logUserIn($user);
        }
    }
}