Ask the client to perform Mojang "joinServer" locally. Verify with Mojang Session Server from the server using a nonce. If verification passes: replace the player's UUID with the official premium UUID ...
1.21.x 1.20.x 1.19.x 1.18.x Earlier versions are not compatible due to the use of new command in the datapack. More recent versions (including snapshots) may be compatible but are not actively ...