You need to have an APP in your Developer Account as described at https://developers.hubspot.com/docs/api/developer-tools-overview
The HubSpot Provider comes with a set of default options:
You can override any of the options to suit your own use case.
import HubspotProvider from "next-auth/providers/hubspot";
The Redirect URL under the Auth tab on the HubSpot App Settings page must match the callback url which would be http://localhost:3000/api/auth/callback/hubspot for local development. Only one callback URL per Client ID and Client Secret pair is allowed, so it might be easier to create a new app for local development then fiddle with the url changes.