Credits - nov/fb_graph GitHub Wiki
See Sample Canvas App.
https://apps.facebook.com/fbgraphsample/ (Canvas App)
https://github.com/nov/fb_graph_sample (Source Code)
app = FbGraph::Application.new(APP_ID, :secret => APP_SECRET)
order = FbGraph::Order.new(ORDER_ID)
order.refund!(:access_token => app.access_token)