Reauth in-game without restarting game and launcher.

If your token expired, you have to relaunch the game and launcher to refresh the login token in order to join online servers. This is more common to microsoft accounts, which the token often expires in a day. Relaunching minecraft for token is very annoying.

How about refreshing the login token without relaunching the entire game?

Let Minecraft communicate with the launcher to get a new token when the login token is expired so you don't need to relaunch entire game. Some 3rd-party mods and clients have already implemented this, but it will be nicer if you can refresh token without these mods!