code: def unsign_url_safe(token, secret_key, salt=None, **kw):
      
      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)
docs: 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: