Verifies the authenticity of a notification message.

        TODO: This is doing a form of authentication and
              this functionality should really be merged
              with the pluggable authentication mechanism
              at some point.

def verify(self, secret_key):
        """
        Verifies the authenticity of a notification message.

        TODO: This is doing a form of authentication and
              this functionality should really be merged
              with the pluggable authentication mechanism
              at some point.
        """
        verification_input = NotificationMessage.SERVICE_NAME
        verification_input += NotificationMessage.OPERATION_NAME
        verification_input += self.timestamp
        h = hmac.new(key=secret_key, digestmod=sha)
        h.update(verification_input)
        signature_calc = base64.b64encode(h.digest())
        return self.signature == signature_calc