def sign_response(self, response):
     from saml2.sigver import sign_statement_using_xmlsec
     response = '%s' % response
     # Sign assertion in the response
     signed_response = sign_statement_using_xmlsec(response, "Response",
                             xmlsec_binary,
                             key_file=os.path.join(path, 'data', 'idp.key'))
     return signed_response