I'd love for Google to figure out something comparable for the Drive API (currently it's not possible to grant read/write access to a single folder; you need to grant access to the entire drive!): https://issuetracker.google.com/issues/36760598?pli=1

I think the fact that the above issue has been open for a very long time is one indication of how difficult and sensitive this type of access control API is. The Google Drive API could be a proving ground for getting the UX right for this (including tricky details like how to manage persistent access to a folder with clear disclosure and user controls).