I find lots of documentation about Single Sign-On whether it be AGO or ArcServer. I find it about federating Portal to ArcServer. What I do not have a clear grasp on is Single Sign-On using the following scenario: I have a multi-machine deployment of ArcGIS Server 10.3.1 with two web adapters. One of which I want to run the secure services through. I would like to use said secured services in ArcGIS Online, and have the users log in only once. So, log in to AGO to see your available apps and maps within your group using an enterprise log in, and then have that permeate down to the web services feeding those apps and maps without having to log in again to use one or more secured services within them. What would be the best approach and methods to use in order to accomplish a single sign on environment between ArcGIS Server and AGO?