validate-auth.json

/* Example assumes your Firepad is at the root of your Firebase Database. */
{
  "rules": {
    "history": {
      ".read": "auth != null",
      "$revision": {
        /* Allow writing a revision as long as it doesn't already exist and  you write your auth.uid as the 'a' field. */
        ".write": "data.val() === null && newData.child('a').val() === auth.uid"
      }
    },
    "users": {
      ".read": "auth != null",
      "$userid": {
        /* You may freely modify your own user info. */
        ".write": "$userid === auth.uid"
      }
    },
    "checkpoint": {
      ".read": "auth != null",
      /* You may write a checkpoint as long as you're writing your auth.uid as the 'a' field and you
         also wrote the revision that you're checkpointing. */
      ".write": "newData.child('a').val() === auth.uid && root.child('history').child(newData.child('id').val()).child('a').val() === auth.uid"
    }
  }
}