Parse the scriptSig and extract the public key.
        Raises ValueError if this is a multisig-controlled subdomain.

def get_public_key(self):
        """
        Parse the scriptSig and extract the public key.
        Raises ValueError if this is a multisig-controlled subdomain.
        """
        res = self.get_public_key_info()
        if 'error' in res:
            raise ValueError(res['error'])

        if res['type'] != 'singlesig':
            raise ValueError(res['error'])

        return res['public_keys'][0]