Multiple Project Configuration for One Web Application

I am developing a web application. I deployed my website to one project and want to get firestore data from another project. So I added two projects configurations in html file. To call the data from second firebase project I declared a variable like below.

var config = {
     apiKey: "<API_KEY>",
     authDomain: "<PROJECT_ID>.firebaseapp.com",
     databaseURL: "https://<DATABASE_NAME>.firebaseio.com",
     storageBucket: "<BUCKET>.appspot.com",
  };

  var secondaryAppConfig = {
      apiKey: "<API_KEY>",
      authDomain: "<PROJECT_ID>.firebaseapp.com",
      databaseURL: "https://<DATABASE_NAME>.firebaseio.com",
      storageBucket: "<BUCKET>.appspot.com",
    };

  var secondary = firebase.initializeApp(secondaryAppConfig, "secondary");

  var secondaryFirestore = secondary.database();

  secondaryFirestore.collection('sample').get().then(snap => {
      var size = snap.size;
      console.log("TotalSample",size);
      // will return the collection size
      document.getElementById('totalStores').textContent = size;
  });

When I wrote a query to get data from secondaryFirestore like above I am getting the error like

error.js:149 Uncaught (in promise) Error: Missing or insufficient permissions.
    at new e (error.js:149)
    at t.fromRpcStatus (serializer.js:93)
    at t.fromWatchChange (serializer.js:573)
    at e.onMessage (persistent_stream.js:391)
    at persistent_stream.js:333
    at persistent_stream.js:308
    at async_queue.js:83

Project-A database rules are like only authenticated people can access the data. I can't change that rules because it is confidential. Actually in both database projects I am signing with same email id. I struct at this point. I tried a lot can't get any idea. Please let me know any idea about how to access the data from secondaryFirestore database.

Thanks in advance.