Apologies for getting late back to you.
You can manage it easily on the cline side by checking the LoggedInUser value. In order to check loggedInUser, please use below code snippet.
If it doesn't contain username than it means user is not loggedIn, so that you restrict on the UI side to not to operate Read/Write operation on the document.
P.S Example code snippet is in Android, if you are working on different platform than let me know it will help us to provide better support to you.
Let me know if it helps.