code: def VerifyServerPEM(self, http_object):
      
      try:
        server_pem = http_object.data
        server_url = http_object.url
  
        if b"BEGIN CERTIFICATE" in server_pem:
          # Now we know that this proxy is working. We still have to verify the
          # certificate. This will raise if the server cert is invalid.
          server_certificate = rdf_crypto.RDFX509Cert(server_pem)
          self.communicator.LoadServerCertificate(
              server_certificate=server_certificate, ca_certificate=self.ca_cert)
  
          logging.info("Server PEM re-keyed.")
          return True
      except Exception as e:  # pylint: disable=broad-except
        logging.info("Unable to verify server certificate at %s: %s", server_url,
                     e)
  
        return False
docs: Check the server PEM for validity.
  
      This is used to determine connectivity to the server. Sometimes captive
      portals return a valid HTTP status, but the data is corrupted.
  
      Args:
        http_object: The response received from the server.
  
      Returns:
        True if the response contains a valid server certificate.