title: angular2 firestore detect document no permissions after subscribing
body: <p>So I have the following piece of code:</p>
  
  <pre><code>this.observable = this.angularFirestore.collection('users').doc&lt;User&gt;(userID).valueChanges();
  this.subscription = this.eventObjectObservable.subscribe((user: User) =&gt;
  {
      //do something here
  });
  </code></pre>
  
  <p>My question is whether it is possible to detect a loss of permissions after subscribing to the document.</p>
  
  <p>For example, after someone visits a page and successfully loads this document and is subscribing to changes, an administrator may remove permissions from this person to access the said document. How can I detect this (shown in console)</p>
  
  <pre><code>"ERROR Error: Missing or insufficient permissions."
  </code></pre>
  
  <p>and handle it accordingly? I am thinking of handle it such that when this event is detected, the said user would get redirected to another page.</p>