CODE EXAMPLE FOR TYPESCRIPT

firestore security rules array-contains

service cloud.firestore {
  match /databases/{database}/documents {
    match /collection/{documentId} {
      // works if `members` = [uid1, uid2, uid3]
      // no way to iterate over a collection and check members
      allow read: if request.auth.uid in resource.data.members;
      // you could also have `members` = {uid1: {}, uid2: {}}
      allow read: if resource.data.members[request.auth.uid] != null;
    }
  }
}