title: FireStore REST API call
body: <p>I am using postman to get data from my firestore api</p>
  
  <pre><code>https://firestore.googleapis.com/v1beta1/projects/myapp-ef511/databases/countries
  </code></pre>
  
  <p>but I am getting this,although my rules are public</p>
  
  <pre><code>{
      "error": {
          "code": 401,
          "message": "Request is missing required authentication credential. Expected OAuth 2 access token, login cookie or other valid authentication credential. See https://developers.google.com/identity/sign-in/web/devconsole-project.",
          "status": "UNAUTHENTICATED"
      }
  }
  </code></pre>
  
  <p>How can I achieve this?I am planning to use retrofit in future.</p>