title: How to restrict others from using your web api except your app users?
body: <p>The users of my app do not need to signup or do anything like that, and they can use the app as soon as they install it on their phone.</p>
  <p>How can I prevent others from using my web apis/services and restrict it only to my app?</p>
  <p>To give a more concrete case, lets say I am using Firebase Realtime Database service. How can I prevent others from using this service on my behalf?</p>