Control relay or LED another Raspberry Pi (not my openHAB server)

Is there there a simple way to control a Raspberry Pi GPIO through openHAB? I have OpenSprinkler on another RasPi and would like to control an unused relay on it using openHAB. In this case I would like to configure an openHAB switch to control GPIO 25. You can see from the OpenSprinkler pinout diagram (below) that this IO is available for use. Is there a way to install something that would respond to a http get command? Or a simple Mosquitto client?