Gets the issuers (from message and from assertion)

        :returns: The issuers
        :rtype: list

def get_issuers(self):
        """
        Gets the issuers (from message and from assertion)

        :returns: The issuers
        :rtype: list
        """
        issuers = []

        message_issuer_nodes = OneLogin_Saml2_Utils.query(self.document, '/samlp:Response/saml:Issuer')
        if len(message_issuer_nodes) > 0:
            if len(message_issuer_nodes) == 1:
                issuers.append(OneLogin_Saml2_Utils.element_text(message_issuer_nodes[0]))
            else:
                raise OneLogin_Saml2_ValidationError(
                    'Issuer of the Response is multiple.',
                    OneLogin_Saml2_ValidationError.ISSUER_MULTIPLE_IN_RESPONSE
                )

        assertion_issuer_nodes = self.__query_assertion('/saml:Issuer')
        if len(assertion_issuer_nodes) == 1:
            issuers.append(OneLogin_Saml2_Utils.element_text(assertion_issuer_nodes[0]))
        else:
            raise OneLogin_Saml2_ValidationError(
                'Issuer of the Assertion not found or multiple.',
                OneLogin_Saml2_ValidationError.ISSUER_NOT_FOUND_IN_ASSERTION
            )

        return list(set(issuers))