A user, group, and device management and authentication system allows administrators to manage one or more directories with devices that are not associated with a domain of the one or more directories via a set of APIs. The system also allows applications and services that do not have direct access to a list of directory users to access the one or more directories. The user, group, and device management and authentication system may be an add-on system that works in conjunction with a centrally-managed directory service to provide such functionality. For example, the system may generate an access token associated with a particular directory that can be used by a service accessed by an administrator to call an API provided by the system. The API call may be translated into a directory-specific API call that can be used to perform an action in the particular directory.