I have used JWT with the Auth0 SaaS as backend on several apps for many years. Auth and user management is a headache I don't need. Never use their SDKs/widgets. Just directly call the HTTP API endpoints from web/node/cli apps.
The downsides of using such a general purpose platform:
Everyone imagines user accounts slightly differently. The result is overly complex/abstract APIs.
It is also a PITA when some Auth0 API is deprecated even though it worked fine for your app. Code rot is no fun.
There is a theoretical concern about long term vendor lock-in. Though so far no problems as they allow export (on any paid plan, IIRC).
I have used JWT with the Auth0 SaaS as backend on several apps for many years. Auth and user management is a headache I don't need. Never use their SDKs/widgets. Just directly call the HTTP API endpoints from web/node/cli apps.
The downsides of using such a general purpose platform:
Auth0 is great. It is hard to stay simple when using a SaaS for something as complicated as user management.