A plugin where my friend cannot join my server using my username?

We are playing on offline mode and he just joins via my username and jumps into lava with my username, please suggest a plugin to stop him from doing that.

Quote from Henery

If your server is in Cracked mode, people can just freely join with any usernames. Consider disabling Cracked mode in Options, or just install any authentication plugin in your server.

Well I play cracked, so If I disable cracked mode then I can't play, so could you suggest an authentication plugin?

Quote from Roman

Try OpenLogin: https://aternos.org/addons/a/spigot/57272

Thanks