In this situation the user ID is the Box identifier for a user. User IDs can be
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.
Using the as-user header has a few requirements. Firstly, the application
needs to be configured to perform actions as users in the Developer
Additionally, the authenticated user needs to be a user with admin permissions,
meaning either an admin, co-admin, or service account. Co-admin users will also
need the 'Manage Users' permission scope. See our guide on User
Types for more details.
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.