Ask HN: Is there a document exchange service for mobile App?

I built a medical app that practitioners uses as a reference. This app has a document exchange module, where user can register and exchange documents with other user of the App.

Basically, a user willing to exchange a document start the app, go to "Send document", takes a picture of the document (like EKG or any medical paper document), then select a recipient in the registry, and hit submit. The recipient receive an email/push notification and can see the document through the App.

I built this using a rails+S3 backend. But this is a lot of IT work and there are features I'd like to add (password reset, 2FA...). I also moved the app to a full single page JS app so the backend doesn't make a lot of sense anymore.

I'm looking for a service, or a collection of service that can provide:

- User management. - User data (users can add notes in the app), a few MB per user is enough. - File upload and sharing for the document exchange module. With proper image handling. - Push notifications for when a user shares a document with you.

The user management part seems easily covered by solution like Auth0. But for the document exchange and push notification I didn't find anything concluant.