Yeah the problem is that using authlib-injector to change the auth on the server is that it only works with that auth server. If you use ely.by it'll only work with ely.by.

That coupled with the fact that Authlib-injector is prohibitively difficult to set up on servers compared to clients is why people running servers meant for non-premium accounts just use offline mode with a password mod.

Also littleskin.cn is another auth server but it seems like it's only used for skins. Theoretically it could be used for servers but it's definitely not it's primary usecase.