Problem with setting up Integrated Windows Authentication with Portal

[JamesMogle]

I've been trying to setup IWA on Portal.  However, every time I try to enter the portal identity store, it fails with the following error:

Error

java.lang.Exception: Could not connect to the user store. Please check the configuration and try again.

Code: 500

I'm also the domain admin.  This is Portal 10.3.1 running on a Server 2012 R2 with an AD in Server 2008 mode.  Any ideas?  Not really getting anything extra in the log.

[BlakeTerhune]

There's a Portal for ArcGIS subspace that would be a better place to post this. Additionally, here's the Esri documentation on the subject in case you may have overlooked something.

Using Integrated Windows Authentication with your portal—Portal for ArcGIS (10.3 and 10.3.1) | ArcGI...

[JakeSkinner]

Just a shot in the dark, but have you tried configuring the identity store with a different user?  You do not need to be the domain admin.