Creates signature for message using specified signer

        :param msg: message to sign
        :param identifier: signer identifier
        :param otherIdentifier:
        :return: signature that then can be assigned to request

def signMsg(self,
                msg: Dict,
                identifier: Identifier=None,
                otherIdentifier: Identifier=None):
        """
        Creates signature for message using specified signer

        :param msg: message to sign
        :param identifier: signer identifier
        :param otherIdentifier:
        :return: signature that then can be assigned to request
        """
        idr = self.requiredIdr(idr=identifier or otherIdentifier)
        signer = self._signerById(idr)
        signature = signer.sign(msg)
        return signature