Gatekeeper

The first time a client joins, the mod creates a unique key pair on its own, without any prompt. The private key stays on the player's computer, and the server keeps only the approved public keys. On later connections the client proves it holds the right key without sending the key itself over the network, so a password guess, a shared secret or a leaked login cannot be reused by someone else.

It suits small offline-mode servers whose operator knows every player in person. A new player waits for approval, and the server checks the presented key against its approved list before letting the player in. Tab completion suggests players awaiting approval to the operator. The operator needs level 3 and the mcgatekeeper.admin permission to manage the gate.

Gatekeeper requires Fabric API. Its server side runs on Fabric or Paper, which speak the same protocol, and Spigot, CraftBukkit and Folia are supported as well. Mod Menu is optional and adds a Gatekeeper Manage Keys screen for viewing stored keys. The server and every player need the mod installed.