shutdown iMac triggered from external system

I am looking to shutdown iMac computers triggered by an external/other system. Its for a fully automated internet cafe, to include iMac's where the "central automation software" can trigger a shutdown of the iMac if the paid time is consumed. With windows/intel PC's it is possible to trigger a shutdown of the PC from another system (cybercafe with a central managed system that triggers the shutdown when the time the customer paid for is fully consumed) My question is, if that is also possible for an iMac. If so, how ?