@nandodixtorsion:Hi there, appreciate the feedback. The scope of the video is security between API Management proxy and the backend API services. I think your question is about securing the subscription-key used between your mobile app and API Management proxy. In that case, one thing you can do is having your mobile app call your app backend first and having the app backend call the APIs.
Let me know if you have further questions. You can find me @miaojiang