def _refresh(self):
        """Refresh the API token using the currently bound credentials.

        This is simply a convenience method to be invoked automatically if authentication fails
        during normal client use.
        """
        # Request and set a new API token.
        new_token = self.authenticate(self._username, self._password)
        self._token = new_token
        logger.info('New API token received: "{}".'.format(new_token))
        return self._token