title: Firebase: User shall only see, what he added to firebase. No one else should see the data of another user. How?
body: <p>The question is formulated pretty much suming up my problem. I somehow cannot figure out, how to achieve this. I guess I would have to add some lines of code to the cloud firestore?</p>
  <p>What would you do?</p>
  <p>At the moment I have a working auth system and a user can add new data and retrieve existing data from the firebase.
  But to point out my issue again: They should only be allowed, to see their own data and post data, which only they can see.</p>
  <p>I really hope someone can help me. Thanks!</p>