title: Flutter Firebase Storage returning FirebaseApiNotAvailableException
body: <p>From a Flutter app, I am trying to determine the download URL of an image within Firebase Storage. For testing, there are <strong>no</strong> auth security rules applied (set as 'allow read, write;') or auth applied in the app. When using the following method, </p>
  
  <pre><code>Future&lt;String&gt; _getDownloadImageUrl(String folder, String filename) async {
    String childpath = "$folder/$filename";
    StorageReference ref = FirebaseStorage.instance.ref().child(childpath);
    Future&lt;String&gt; durl = await ref.getDownloadURL();
    return durl;
  }
  </code></pre>
  
  <p>I get the following error (when testing on Android device) :</p>
  
  <blockquote>
    <p>E/StorageUtil(): error getting token
    java.util.concurrent.ExecutionException:
    com.google.firebase.FirebaseApiNotAvailableException: firebase-auth is
    not linked, please fall back to unauthenticated mode.</p>
  </blockquote>
  
  <p>The same app is querying (Firestore) database data OK (with no auth), but I'm not sure if I am missing a step, for example, such as explicitly performing an action relating to "unauthenticated mode" for Firebase Storage?</p>