There's probably a real business opportunity in selling a product that abstracts this plumbing into an SDK for developers, so they can give their users a polished flow for authenticating and configuring the storage on the frontend, and then interact with the user's chosen directory on the backend. I imagine it's been done before with various "file upload" products but I'm not familiar with the space.

As a user, I would love this kind of integration because it means data portability is built into the product.