code: def create_identity_from_private_key(self, label: str, pwd: str, private_key: str) -> Identity:
          
          salt = get_random_hex_str(16)
          identity = self.__create_identity(label, pwd, salt, private_key)
          return identity
docs: This interface is used to create identity based on given label, password and private key.
  
          :param label: a label for identity.
          :param pwd: a password which will be used to encrypt and decrypt the private key.
          :param private_key: a private key in the form of string.
          :return: if succeed, an Identity object will be returned.