Update: Oct 2019. Leveraging the SailPoint IdentityNow API's is now easier using the SailPoint IdentityNow PowerShell Module. Also see this post for how to generate v2 and v3 API credentials.
UPDATE: 18 Dec 2018 Please see this new post on accessing v3 / non-published SailPoint IdentityNow API's using PowerShell.… keep reading