For a personal webapp accessed from a few devices I just keep a list of session IDs in the app's config file. The web framework generates the session id, it's derived from a cookie with no expiry.

There's a "/register" page that just has a mailto: link to email myself, with the session ID in the mailto email body parameter. Easy to copy-paste into the config file when setting up a new device.

This is probably less useful for external users (who want to log in extra devices themselves), but something similar might work.