Can anyone clarify which version of the .NET Framework we should use when building a custom authentication provider for GroupShare 2017?

Romulus' blog post states v4.5.2 but that was written for GroupShare 2015.

He also mentions that the project should reference two SDL assemblies - I first of all tried building a project against v4.5.2 with those referenced assemblies but it wouldn't build until I changed the project to v4.7.2. I decompiled those assemblies and found that they were built for v4.7.2.

So I built the custom authentication provider against .NET Framework v4.7.2 and got it signed. But when I drop it into place on the server, along with the accompanying *.plugin.xml file, I can't log-in.

Furthermore, my custom authentication provider should record attempts in a log file and the log file isn't even being created, so it looks like there isn't a bug inside the custom provider but outside - i.e., in the building of it.

I've also checked Windows' Event Viewer but there are no errors recorded around the time of my log-in attempts.

And I've decompiled a few other Sdl.*.dll files in the same folder and found that some are v4.5.2 and others are v4.7.2 - my guess is that maybe different GroupShare services use different versions of .NET?

So which is it for the custom authentication provider, v4.5.2 or v4.7.2? If the former then how can I reference those two SDL assemblies which were built against v4.7.2, and if the latter then...  any ideas why mine isn't being implemented on GroupShare?