title: flutter firebase_auth OAuth exception: errorMessage: (#803) Cannot query users by their username (CHANGE-ME)}
body: <p>I'm new to flutter and attempting to add firebase_auth GoogleSignIn to my app.  I've followed the instructions of about 5 samples I've found online but keep getting the error when I run the app:</p>
  
  <pre><code>E/GraphResponse( 8321): {HttpStatus: 404, errorCode: 803, subErrorCode: -1, errorType: OAuthException, errorMessage: (#803) Cannot query users by their username (CHANGE-ME)}
  </code></pre>
  
  <p>I've posted the code for my app here for review:  git@github.com:naustin/servicereport_autherror.git</p>