[motohagiography]

If you needed to auth users on both a mobile app across platforms, and a browser, it makes sense to store and xmit user session information in a JWS or JWE, using it as an abstraction which you can serve as a cookie to the browser, and handle consistently across apps. If you get into multifactor auth, implementing it in JWT becomes more useful. A full OAuth provider seems heavy for what you've described.