title: Flutter - Understanding Firebase Admin and how to get a user's information from email/uid/name
body: <p>I'm making a little Snapchat clone, and a part of this app I'm trying to build is the ability to add a friend and start a conversation with them. I'm using Firebase to manage my users and I'm a little stuck now trying to figure out what works and why I'm getting problems trying to use some methods or functions.</p>
  <p>What I want is this simple line of code to work:</p>
  <pre><code>var userByEmail = await _admin.app().auth().getUserByEmail(&quot;b@gmail.com&quot;);
  print(userByEmail.toString());
  </code></pre>
  <p>However this has been giving my some problems, most recently, the following error message:</p>
  <blockquote>
  <p>Unhandled Exception: FirebaseAuthError(auth/invalid-credential): Must initialize app with a cert credential or set your Firebase project ID as the GOOGLE_CLOUD_PROJECT environment variable to call verifyIdToken().</p>
  </blockquote>
  <p>Getting to this point made me want to first ask a question about FirebaseAdmin and Auth before continuing and potentially screwing up my app settings.</p>
  <p>Is there a simple way to do what I'm trying to do?</p>
  <p>I have a Firebase.instance.initializeApp() in my Main function, do I only ever call that once or should I start initilizeApp in the initState of each Stateful Widget where needed?</p>
  <p>What does this error message actually mean?</p>