protected function resolveUser($user)
    {
        if ($user instanceof UserInterface) {
            return $user;
        }

        if (is_integer($user)) {
            $user = $this->sentinel->findById($user);
        } else {
            $user = $this->sentinel->findByCredentials([
                'email' => $user
            ]);
        }

        return $user ?: false;
    }