My organization has a project that in the past has been able to function without issue with just the Google Drive and Google Picker APIs. Recently, (within the last few weeks?) I now get 403 errors that enabling the Admin SDK API is required.
Admin SDK has not been used in project XXXXXX before or is disabled. Enable it by visiting https://console.developers.google.com/apis/api/admin.googleapis.com/overview then retry. If you enabled this API recently, wait a few minutes for the action to propagate to our systems and retry.
The project does make a request to the admin api (https://www.googleapis.com/discovery/v1/apis/admin/directory_v1/rest) along with its request to the drive api, but it's been doing that for years without needing to enable the Admin SDK API, and we've made no code changes there. Did something change recently around when the Admin SDK API is required?
(The project does have a service account, domain-wide delegation is enabled, etc.)