Whenever I tried to add a secure service to Portal for ArcGIS as a new item, I get an error message. The message will vary depending on what type of service it is, but for ESRI's routing service, for example, I get "Error Generating Token". I've also tried to create a helper service proxy item according to the instructions: Add premium helper services—Portal for ArcGIS (10.3 and 10.3.1) | ArcGIS for Server, but this yields the same result. All of the services I am trying to add can be added to ArcGIS Desktop without problem, so I've been focusing on the forward proxy settings for Portal. I have configured Portal for our forward proxy according to the instructions I could find, but I am not sure if it is working. I have a support ticket open with ESRI, but I am wondering if anyone else has successfully overcome this kind of issue.