To log on with Lantern to the Chessclub anonymously input the username and password as normal but place a ! (explanation point) before the username. I.e. !rookers rather than rookers and then the password.
To log on with Lantern to the Chessclub as a guest input the handle as either g or guest and do not enter a password.
As of Lantern version 5.76, there is now a guest button next to 'Ok' that can be clicked as well to login as a guest. This wont reset the user's saved name and password.