If you are extending the user access token then the page token received will not have an expiry date. So then the user will only have to login once in the entire usage of the app.
Exchange the short-lived user access token for a long-lived access token using the endpoint and steps explained earlier. By using a long-lived user access token, querying the [User ID]/accounts endpoint will now provide page access tokens that do not expire for pages that a user manages. This will also apply when querying with a non-expiring user access token obtained through the deprecated offline_access permission.
https://developers.facebook.com/roadmap/offline-access-removal/