code: def sign_data(self, data, expires_in=None, url_safe=True):
          
          if url_safe:
              return utils.sign_url_safe(data,
                                         secret_key=self.secret_key,
                                         salt=self.user_salt,
                                         expires_in=expires_in)
          else:
              return utils.sign_data(data,
                                     secret_key=self.secret_key,
                                     salt=self.user_salt,
                                     expires_in=expires_in)
docs: To safely sign a user data. It will be signed with the user key
          :param data: mixed
          :param expires_in: The time for it to expire
          :param url_safe: bool. If true it will allow it to be passed in URL
          :return: str -  the token/signed data