Thanks, Jake. That got my web adaptor configured.
I had it working this morning -- all of my setup completed, ArcGIS Server federated with the portal -- I had just not set up HTTPS. I was able to add a zipped shapefile to the portal, created a hosted feature layer, and added it to the portal's map viewer. Then, I rebooted the machine.
Now, I'm stuck again. Since ArcGIS Server is now federated with the portal, it authenticates through the portal, but something's not right.
If I try to log in to the Portal through the Web Adaptor (https://, the request gets redirected to the internal URL (https://<servername>.localdomain:7443/arcgis/home). If I try to validate the federated servers from the portal, validation fails. If I try to add a new one, I get an error indicating that federation of servers is disabled when accessing the portal without using the web adaptor. So, I go back to try to re-configure the web adaptor. I get various errors depending on what URL I try for the portal:
https://<servername>.local:7443 : "Failed to get administrator token from Portal. Please verify that the Portal URL specified can be accessed successfully."
http://<servername>.local:7443 : "Failed to get administrator token from Portal. Please verify that the Portal URL specified can be accessed successfully."
https://<servername>.localdomain:7443: "Unable to configure the Portal with the Web Adaptor. Please make sure that the Portal and WebAdaptor are of the same version."
http://<servername>.localdomain:7443: "The server committed a protocol violation. Section=ResponseStatusLine"
This is very frustrating! I've been banging at this since Friday, trying to do something which should be very simple: set up a base install of ArcGIS Enterprise on a single VM using the ArcGIS Enterprise Builder and it. doesn't. work!