When integrating with oauth2, I think it's more common to use strapi as resource server instead of client(strapi is headless). It's the duty of frontend (like nextjs) to get user authenticated and obtain the access token which used in Authentication header when access strapi, what strapi should do is validate access token and get user info from it. This make strapi more easy to integrate with other backend.

see: https://github.com/strapi/strapi/issues/12207