$userId = User::checkUserData($email, $password);

public function actionLogin() {

    $email = '';
    $password = '';

    if (isset($_POST['submit'])) {
        $email = $_POST['email'];
        $password = $_POST['password'];

        $errors = false;

        $userId = User::checkUserData($email, $password);

        if ($userId == false) {
            $errors[] = "Неверные E-mail или пароль.";
        }
        else {
            User::auth($userId);

            header("Location: /cabinet/");
        }
    }

    require_once ROOT.'/views/user/login.php';

    return true;

}

public static function checkUserData($email, $password) {

    $db = Db::getConnection();

    $sql = "SELECT * FROM user WHERE email = :email AND password = :password";

    $result = $db->prepare($sql);
    $result->bindParam(':email', $email, PDO::PARAM_STR);
    $result->bindParam(':password', $password, PDO::PARAM_STR);
    $result->execute();

    $user = $result->fetch();
    if ($user) {
        return $user['id'];
    }

    return false;

}