Retrieve Firebase data/uid from Google Script

Question

My Firebase Realtime Database is Structured root{users{$uid{...}}} so that I can use the following Firebase Security Rules.

{
 "rules": {
   "users":{
     "$uid":{
          // Allow only authenticated content owners access to their data
       ".read": "auth.uid == $uid",
       ".write": "auth.uid == $uid"
      } 
    }
  }
}

I am posting data using the REST API and I obtained the uid using Sign in with OAuth Credential https://firebase.google.com/docs/reference/rest/auth#section-sign-in-with-oauth-credential

The Problem

1. In a Google Script, using my developer account, which is also the owner of the Firebase Realtime Database, the following code works.

let database = FirebaseApp.getDatabaseByUrl('https://[app-id].firebaseio.com/users/[hardcoded-uid]',ScriptApp.getOAuthToken());
 console.log(database.getData(""));

where FirebaseApp is a connected library whose source code can be found here https://sites.google.com/site/scriptsexamples/new-connectors-to-google-services/firebase/source. And actually, using the developer account, it doesn't even matter if the part of the database I try to access follows the security rules.

However, when I test it using my personal account, with that account's uid hardcoded in, I get the following error.

Error: Unauthorized request.
FirebaseApp_._sendAllRequests   @ Code.gs:647
FirebaseApp_._buildAllRequests  @ Code.gs:520
baseClass_.getData  @ Code.gs:224

Question: How can I access Firebase data for accounts that are not the database owner, ideally using ScriptApp.getOAuthToken()?

2. Even if I could solve question 1, I do not know how to get the database uid in the Google Scripts environment. I would like the use SpriptApp.getOAuthToken() for the access token. When I try obtaining the uid using the same REST API call as above (Sign in with OAuth Credential), I get the error

"INVALID_IDP_RESPONSE : Invalid Idp Response: access_token audience is not for this project"

let body = {requestUri:"https://app-settings.fitbitdevelopercontent.com/simple-redirect.html", postBody:"access_token="+ScriptApp.getOAuthToken()+'&providerId=google.com', returnSecureToken:true, returnIdpCredential:true};
  let response = UrlFetchApp.fetch("https://identitytoolkit.googleapis.com/v1/accounts:signInWithIdp?key=[key]", {
    'method': 'POST',
    // headers: {
      'contentType': 'application/json',
    // }
    payload: JSON.stringify(body),
  })

Question: How can I get a Firebase database uid in Google Scripts, using ScriptApp.getOAuthToken()?

Answer 1

等待大神答复