In the Authorization Code Flow, how can I let my backend know a user is authenticated and authorized?

I’ve successfully implemented the Authorization Code Flow to the point where my frontend can log a user in, verify authentication, retrieve user profile information, and retrieve what I understand to be an opaque token by running Auth0Client’s getTokenSilently() method.

However, now I’d like to hit my backend API endpoints with the confidence that the user has been authenticated/authorized via Auth0. From what I understand, opaque tokens are not decodable. How can I do this?