How to authenticate from my middleware after user logs in on web client

Hi, I have a web app that uses Realm and Realm.LogIn with email/password. This works and I receive the user object and access/refresh tokens. Now, when I call one of my own API endpoints, say, how do I authenticate the logged in user from my Node app middleware?

My Node app runs as a CloudFlare worker. I can pass it the access/refresh tokens in headers or even the body of every request to my own API. But, once my Node app receives the session/user tokens, how do I then instantiate and call Realm services with the user’s tokens?

My Client

  var response = null;
            this.user = await this.RealmApp.logIn(credentials).then(res => {
                response = res;
            }).catch(error => {
                console.log("ControllerDatabase: LogIn error is - " + JSON.stringify(error));

My Node Server App

// How do I authenticate to Realm
var userSession = {
   accessToken: "tokenPassedFromMyWebClient",
   refreshToken: "tokenPassedFromMyWebClient"
// ...  how to auth ... ?

// After auth, get some data from Realm
const col = this.TheAtlasDB.collection(collection);
            if (col) return await col.findOne(query);    
            return null;