From the API, you could also try to use the search API. This will return the users and their attributes:
You can call the Search API directly or you can also use the SDK as I did here:
The nice part of the SDK is that it will handle the authentication and the pagination directly.
Also, you might find this presentation by Yannik Beot helpful. Yannik built a custom connector to ISC for PowerBI.
BYOB - bring your own BI - Content / Video Library - SailPoint Developer Community