This is pretty new too...I guess macOS Sierra is trying to keep us safe...

@donmontalvo
is that you testing the tethered caching in 10.12.4? if so what are your thoughts..Oh and no Deadpool pic?
Ahh that makes sense, saw the feature but didn't get a chance to read up on it.
https://www.youtube.com/watch?v=ptKgRecPi1I
Hi folks, Apple have a KB on this: here
Seems the key is not settable with a profile, but script should work.
So it looks like that should only need to be done once per computer and it should stick indefinitely....
@bentoms saves me again - thanks! I also put a ticket in with apple asking for profile setting for this. # 100184809914 if anyone wants ti piggy back
@CasperSally NP, it would be really useful to know what Apple classifies as an "Unknown" server.. we've seen the same with folks & Kerberos tickets.
Simple one liner seems to take care of the pop-up for All users on the machine, fresh users as well as existing. works well in our labs that we just updated to 10.12.6
sudo defaults write /Library/Preferences/com.apple.NetworkAuthorization AllowUnknownServers -bool YES
I tried to make a config profile based on the com.apple.NetworkAuthroization.plist file but it seems to not work. Once I created the plist by using the suggested terminal string mentioned by @ChicagoGuy1984 the server connection message is suppressed. Has anyone been able to make a config profile and it work?