That depends on what your definition of authentic is. If it means ingredients sourced from their host countries, then that's going to make it extremely hard for any restaurant to start; considering the logistical cost and generally things not being fresh enough. The appropriate definition should be authentic methods. If I want to cook dum biryani and market it as dum biryani, I should be cooking it in the traditional method of using a bread sealed handi; but calling it unauthentic if my chicken wasn't born in Hyderabad makes no sense.