To sign url safe data.
    If expires_in is provided it will Time the signature
    :param token:
    :param secret_key:
    :param salt: (string) a namespace key
    :param kw:
    :return:

def unsign_url_safe(token, secret_key, salt=None, **kw):
    """
    To sign url safe data.
    If expires_in is provided it will Time the signature
    :param token:
    :param secret_key:
    :param salt: (string) a namespace key
    :param kw:
    :return:
    """
    if len(token.split(".")) == 3:
        s = URLSafeTimedSerializer2(secret_key=secret_key, salt=salt, **kw)
        value, timestamp = s.loads(token, max_age=None, return_timestamp=True)
        now = datetime.datetime.utcnow()
        if timestamp > now:
            return value
        else:
            raise itsdangerous.SignatureExpired(
                'Signature age %s < %s ' % (timestamp, now),
                payload=value,
                date_signed=timestamp)
    else:
        s = itsdangerous.URLSafeSerializer(secret_key=secret_key, salt=salt, **kw)
        return s.loads(token)