This is the Forge version of ReAuth, the Fabric version has been split off and is available here.

It is now possible to use Microsoft accounts with ReAuth in 1.7.10 through 1.19
1.4.7-1.7.2 versions may come at a later time

Overview:

Fixes the Problem of having to restart your Client when your Session is invalid
Shows you wether your Session is valid
Login and retry for failed connection attempts
Change Accounts while Minecraft is running
Change Username for playing offline

Description:

This Mod is Clientside only - it will have no effect in a servers mod folder.

While entering your Logindata into a "random" Mod might sound risky, you are more than welcome to look at the code yourself.
To that end the Code is visible on Github; a Java-Decompiler (JD-GUI) is available here.

You are free to include this Mod in any Modpack as long as the Mod is not modified and the ModPack is distributed free of charge and in accordance to Mojangs EULA.

Features:

The Multiplayer Screen now features a Session indicator at the top: If it's red you'll have to log in again.
On the Login Screen you can login and optionally save your password to config. Please bear in mind that, while the credentials are encrypted before being saved to config, a malicous programms may still gain access to your password that way. The Encryption is AES based with the Key derived from the Files Location, Symlinks may be used to relocate the config or share it between instances.
If a connection to a server fails because of an invalid session, two buttons are added to error screen. The first allows for opening the Login Screen. The other provides a quick "login and retry" functionality, when credentials are saved to config.
From 1.7.2 onwards a hidden button is available in the MainMenu (id 17325) for use with CustomMainMenu.

Multiplayer Screen with Valid Session