Generate an access token with a client/access token pair. Used
        access token is invalidated.

        Returns:
            dict: Response or error dict

def refresh(self):
        """
        Generate an access token with a client/access token pair. Used
        access token is invalidated.

        Returns:
            dict: Response or error dict
        """
        endpoint = '/refresh'

        payload = {
            'accessToken': self.access_token,
            'clientToken': self.client_token,
        }
        rep = self._ygg_req(endpoint, payload)
        if not rep or 'error' in rep:
            return False

        self.access_token = rep['accessToken']
        self.client_token = rep['clientToken']
        self.selected_profile = rep['selectedProfile']
        return True