I host my own Minecraft server and have online-mode set to false in serer.properties.
Now, I want others to join but I don’t expect them to buy a legitimate copy of Minecraft. Isn’t that why we use this setting online-mode?
In the ol’ days (1.8 and post), I remember using some copy of Minecraft where I could just change my username on every start of this client, and join my server. Period. Done. I want the same again. Is this possible? In a non-illegal way? What about grey-area? I don’t care about security or impersonation (partly).
Just adding to this, this is because when online mode is enabled, the UUID is given to the server from the Minecraft authentication server. When it is disabled, the UUID is generated from the username.