Custom player class

ConnectionManager#setPlayerProvider sets which object is constructed for each connecting player. A subclass of Player can override default behavior or hold additional state:

public class CustomPlayer extends Player {
    public CustomPlayer(@NotNull PlayerConnection playerConnection, @NotNull GameProfile gameProfile) {
        super(playerConnection, gameProfile);
    }
}

MinecraftServer.getConnectionManager().setPlayerProvider(CustomPlayer::new);

Assigning your own UUID

The provider also sets the player's UUID. Constructing a new GameProfile replaces the one Minestom generated, allowing a UUID from your own database or registration system:

MinecraftServer.getConnectionManager().setPlayerProvider((connection, gameProfile) -> {
    UUID uuid = ...; // look up your own identifier for gameProfile.name()
    return new Player(connection, new GameProfile(uuid, gameProfile.name(), gameProfile.properties()));
});

WARNING

The client has already been sent its UUID by the time the provider runs, in every auth mode. Minestom uses the overridden one from here on, but the two no longer agree. To change the UUID the client is told, use AsyncPlayerPreLoginEvent#setGameProfile, which fires early enough.