title: How to get authenticated users from firebase database?
body: <p>I'm creating app where I will be using Firebase messaging service. Messaging is  working fine, but now I wish to make it happen between two users. </p>
  
  <p>I believe I need to provide a authentication  for each user then search for their connections(their friends  via their social network connections or their mail ids). </p>
  
  <p>I managed to create Google+ authentication in my app using Auth.GOOGLE_SIGN_IN_API and AppInvite.API, but connecting to other users in firebase had no clue, then I went through these links <a href="https://classroom.udacity.com/courses/ud0352/lessons/daa58d76-0146-4c52-b5d8-45e32a3dfb08/concepts/d053c636-9d48-43a6-ba05-5db4781dc562" rel="nofollow noreferrer">Udacity tutorial</a> and <a href="https://codelabs.developers.google.com/codelabs/firebase-android/#10" rel="nofollow noreferrer">Codelabs tutorial</a> and the <a href="https://firebase.google.com/docs/auth/android/google-signin" rel="nofollow noreferrer">Firebase  guides</a>. (The tutorials explained the same thing and every one authenticated using the email provider, and not via the Google+ signin. And as a matter fact when I initially tried Google+ signin via these procedures, it didnt work, but email provider is working.)</p>
  
  <p>Anyways email provider is also good for me as of now but still don't have a clue how to connect two users thriugh Firebase. I connected two users, its showing in my Firebase authentication console but how to connect two user one to one?</p>
  
  <p>Any clues??</p>