docs: def signingPayloadState(self, identifier=None):
          """
          Special signing state where the the data for an attribute is hashed
          before signing
          :return: state to be used when signing
          """
          if self.operation.get(TXN_TYPE) == ATTRIB:
              d = deepcopy(super().signingPayloadState(identifier=identifier))
              op = d[OPERATION]
              keyName = {RAW, ENC, HASH}.intersection(set(op.keys())).pop()
              op[keyName] = sha256(op[keyName].encode()).hexdigest()
              return d
          return super().signingPayloadState(identifier=identifier)