Neo Auth is a NeoForge version of the Auth Me mod by Axieum , it allows you to authenticate and re-validate your Minecraft session in-game.
To quote the the original mod (Auth Me):
A Minecraft mod that brings account authentication into the game in the efforts of overcoming the infamous session validation error when connecting to a server.
NeoAuth is built specifically for the NeoForge mod loader, unlike the original Fabric-based Auth Me. While retaining nearly all functionality of Auth Me, it excludes offline authentication in this NeoForge version.
Like Auth Me, NeoAuth is a client-side-only mod.