TUTORIAL: Follow the steps below to define your ClientID in your client. 1- Correct File Location (minecraft\client\multiplayer\GuiConnecting.java) 2- Find this line between lines 63 and 75. (The number of lines may vary.) 3. Paste the code I gave to the GuiConnecting line. (Sample image.)
default = your client token you need to change this and create a custom token, it supports special characters. (Do not share your client token with anyone!)
4. After you are done with the client side, open the config.yml file and place the token you created in the default place of the "ClientID: default" section.
5. And restart your server, that's it! Your server is now logged in from a special client!