code: def expiration_datetime(self):
          
          expires_at = self.get('expires_at')
          if expires_at is None:
              # consider it is expired
              return dt.datetime.now() - dt.timedelta(seconds=10)
          expires_on = dt.datetime.fromtimestamp(expires_at) - dt.timedelta(seconds=EXPIRES_ON_THRESHOLD)
          if self.is_long_lived:
              expires_on = expires_on + dt.timedelta(days=90)
          return expires_on
docs: Returns the expiration datetime
          :return datetime: The datetime this token expires