In this situation the user ID is the Box identifier for a user. User IDs can
found for any user via the GET /users endpoint, which is only available to
admins, or by calling the GET /users/me endpoint with an authenticated user
session.
The application must be configured to perform actions as users in the
Developer Console.
Additionally, the authenticated user needs to be a user with Admin permissions,
meaning either an Admin or Co-Admin. See our guide on
User Types for more details.
You cannot use the user_id of
Service Accounts
in the as-user header.
Please note that some of our SDKs create new clients for the other user, while
others modify the existing client and provide a way to return to a state where
the client authenticates for the original user itself.