How to verify that a connection to the server comes from an app with Ionic/AngularJS/Cordova?

A system needs to be created composed of:

1. An app that runs in a smartphone (iOS and Android) that connects to a backend server.
2. A backend server offering a web service (REST).

What is needed is a way to verify that the internet traffic that the backend server receives comes from the app. (Why is this needed ? Because the app will only connect to the backend server at most every hour, so the backend server doesn't get overloaded with too many requests).

If Ionic with AngularJS in Cordova is used, how can that be achieved ?

The proposed solution up to this moment is to embed a digital certificate in the app and that digital certificate is used to validate with the server (This idea is like a Java Applet that runs in a browser and use a digital certificate in the local computer to validate with the server) .

Can this be done with Ionic/AngularJS/Cordova ? I was looking to the documentation and many videos and I couldn't find anything about this.

Thank you for any answer.