About 20 years ago when I was a teenager Microsoft did this in my country with rock-paper-scissors. XML-RPC-based web services were new at the time and they promoted it this way. You hosted your own web service and they called it to play, I think 10 or 20 games against each opponent in your group. Obviously you can't get an edge against someone playing completely randomly but they placed a bunch of simpler bots in the groups that you could detect (e.g, always playing a pattern). Group winners made it to the final. It was awesome, thanks for reminding me of that memory!