What are the options for Rewarded Video Ads if one developing game in WebGL within Unity3D?

I searched internet and there were not any useful links. Some said to use Ad Sense but i think it is against facebook policy if it is to be published to FB Canvas(Correct me if i am wrong). Are there any plugin that are available? Or Is there any way to set it up externally outside unity and reference them using Application.ExternallCall.