database.rules.json

{
  "rules": {
    ".read": true,
    ".write": false,
    "ratings": {
      ".read": false,
      ".write": false,
      "$uid": {
        ".read": "auth.uid === $uid",
        ".write": "auth.uid === $uid"
      }
    },
    "userSessions": {
      ".read": false,
      ".write": false,
      "$uid": {
        ".read": "auth.uid === $uid",
        ".write": "auth.uid === $uid"
      }
    },
    "speakers": {
      ".read": true,
      ".write": "root.child('users').child(auth.uid).child('rules').child('speakers').val() === true"
    }
  }
}