Read the first couple of posts and you should be good to go:
Official Alexa Smart Home Skill for openHAB 2
Edit: okay, HUE emulation is a different story, take a look here:
https://docs.openhab.org/addons/ios/hueemulation/readme.html
and you need to tag your items with “Switchable” or “Lighting” according to the homekit syntax: