Plug in Yggdrasil

Mythic Mirror speaks Yggdrasil. Point authlib-injector at it and offline-server clients load your skins.

Server (Java)

java -javaagent:authlib-injector-1.2.x.jar=https://<your-domain>/authserver -jar server.jar

Key endpoints

Endpoint	Purpose
GET /	Root meta (skinDomains, signaturePublickey)
POST /authserver/authenticate	Exchange a player name + that player’s launcher password for a token (the site password is not accepted here — see ADR-0012)
POST /sessionserver/session/minecraft/join	Record the serverId session
GET /sessionserver/session/minecraft/hasJoined	Server fetches the profile
GET /sessionserver/session/minecraft/profile/{uuid}	Signed profile

Mojang requires the textures property signature from 1.19+. Mirror signs it with an RSA-2048 key (see ADR-0008).