Is there are an option to get field expires instead of expires_in - to get token from Fitbit?

[umbrella-georgiy-mikhailov]

Hi all! Is there are an option to get field expires (like timestamp) instead of (or with) expires_in - to get token from Fitbit? If yes, would you please describe how to use expired field?

Some background

Our solution - client-server. Token uses expires_in value (as it is said in Fitbit documentation - link). Although our API (backend) requests us to use expires value for the token. Documentation or how-to work with expires (instead of expires_in) for the token in Fitbit we couldn't find. Any help would be highly appreciated.