I use to be able to authenticate as the subject_type user on the client id app 

kox474mes4cugrj929i4kh5enokukmlt

This is a free account and the app is authorized and enabled.

However, now it seems that the subject_type is being required to be set to enterprise. The problem with this is that as the enterprise, I have to add the "Automationuser" to the folder I want the user to upload to. This is a problem because I have been shared several folders and it would be a large coordination effort to have everyone add the "Automationuser" as an uploader. And this would break for any new shares if the user wasn't added.

Is there a way to still be able to upload as the user that has access to those folders? I tried using the As-User header, but then that returns the error like the folder doesn't exist.