Thanks @dan.woda I always forget to mention that side of things, whoops!
Going back to the Access Token, I forgot to mention you should be able to access that Token from an authenticated session using the Auth0\SDK\Auth0::getAccessToken() method, but it is the token in it’s “raw” JWT format — it isn’t decoded like the ID Token is for you. You should be able to run it through the Auth0\SDK\Auth0::decode() method to get to the data you’re looking for, though. More on that here: GitHub - auth0/auth0-PHP: PHP SDK for Auth0 Authentication and Management APIs.