title: how to prevent anonymous user to perform some actions via Firestore security rules?
body: <p>I want to ensure that only non anonymous user that can create events in my Firestore database. but how to do that in Firestore security rules ?</p>
  
  <pre><code> match /events/{eventID} {
  
        allow create: if isSignedIn() &amp;&amp; if isNonAnonymous()
  
  
  }
  
  function isSignedIn() {
        return request.auth != null;
  }
  
  function isNonAnonymous() {
      // what should I write in here ?
  }
  </code></pre>