Actually since OpenSprinkler supports HTTP station, you can already use OSBee as a remote station, because you can send HTTP GET command to it to open/close a valve. So the easiest way is to set an OpenSprinkler station as a HTTP station, and type down the command needed to open/close a valve on OSBee. The OSBee API is available at:
https://github.com/OpenSprinkler/OSBeeWiFi-Firmware/tree/master/docs