JarsAuth

JarsAuth authenticates players on servers that run offline mode, where identity normally rests on the username alone. A dedicated authentication step stops another player from logging in under a name already in use. The login server checks each player's license, and a connection is denied when the license fails. Licenses are revalidated periodically during gameplay, so a session is not checked only once at join time.

The mod suits servers that want players to use only a modpack provided by the server. Server owners can set a fine-grained whitelist, and the server-side configuration is stored in a SQLite database. Version 6.0 moved settings from scattered config files into that database, and a built-in configuration tool is included with the mod. The schema is identical across versions, so a migration between releases is straightforward.

JarsAuth is published for Fabric, Forge and NeoForge across 13 release versions, 1.16.5 – 1.21.11, and is licensed under the GNU General Public License v3.0 only, so the code is open source. Client and server both need the mod, and clients must update their client-side configuration. Upgrading from 5.x means regenerating the server-side configuration files, since 5.x carries a critical bug that drives CPU usage abnormally high and 6.x is the line to use.