[Ogre]

"Moving left" is NOT an input. An input is "The controller is pushed to the left" (with perhaps a numeric value of how far it is pushed to the left). "Firing once" is similarly NOT an input. "The fire button is down" and "The fire button is up" are inputs. That is how well implemented first person shooters have worked since the Quake days (I think Quake 2 actually).

The point of the article is actually that the server doesn't validate anything. There's nothing to validate. The only data it gets from the client is the state of the controls. Then it runs the real simulation. The client only ran a prediction of what it thought the server would do. Sometimes, it's wrong and corrects itself when it gets new values from the server.