The code I linked to can be run in Auth0 as a Rule. Rules are javascript snippets that run (only!) when a user logs in. Alternatively you could use a hook to run the same code during user registration.
You can query the /userinfo endpoint for user information, but you can also just include arbitrary data from the user’s profile in your ID and / or access tokens by writing a rule that handles that. For example, the following rule adds the uuid, created by the previous rule, to the ID token:
This diagram may be helpful as well:
