Update: Oct 2019. Leveraging the SailPoint IdentityNow API's is now easier using the SailPoint IdentityNow PowerShell Module.
UPDATE: 5 Oct 2018 Please see this new post on accessing v1, v2 and non-published SailPoint IdentityNow API's using PowerShell. The details in this post will still work for v1 API's.… keep reading