title: Firebase Firestore prevent client side creation of fields in a document
body: <p>I am struggling to find a solution to prevent clients from just creating random fields with values in a document where they have write access to in Firestore. Since you cannot restrict access to single fields in Firestore like you could with the realtime database, this seems hard to achieve.</p>
  
  <p>A solution would maybe be to not allow creation of fields and just letting clients update fields, but this would mean you would have to precreate the fields for documents which is not really a good solution in my opinion, especially if you have documents per user, which are dynamically created and having to use cloud functions to precreate fields in a document just seems unjustified.</p>
  
  <p>Does anyone have a better solution?</p>