code: def validate_signature(self, signedtext, cert_file, cert_type, node_name, node_id, id_attr):
          
          if cert_type != 'pem':
              raise Unsupported('Only PEM certs supported here')
  
          import xmlsec
          xml = xmlsec.parse_xml(signedtext)
  
          try:
              return xmlsec.verify(xml, cert_file)
          except xmlsec.XMLSigException:
              return False
docs: Validate signature on XML document.
  
          The parameters actually used in this CryptoBackend
          implementation are :
  
          :param signedtext: The signed XML data as string
          :param cert_file: xmlsec key_spec string(), filename,
              'pkcs11://' URI or PEM data
          :param cert_type: string, must be 'pem' for now
          :returns: True on successful validation, False otherwise