One eliminates a problem on to run into the next one
CUPS worked on the server and prints just fine, but it did not want to print from Windows 10.
resulted in "Windows cannot connect to printer" and "Returning HTTP Forbidden for Get-Printer-Attributes" in the CUPS error_log.
Manually changing the cupsd.conf file fixed the problem, but I am afraid this will be overwritten eventually:
# Deny From All # this was the default I commented out
Allow From 127.0.0.1 # I am not sure if this is necessary
Allow From 192.168.10.0/255.255.255.0 # this is my local network
While looking further into the CUPS error log I found the following:
E [11/Mar/2017:12:19:29 -0500] Unknown directive BrowseOrder on line 5 of /etc/cups/cupsd.conf.
E [11/Mar/2017:12:19:29 -0500] Unknown directive BrowseAllow on line 6 of /etc/cups/cupsd.conf.
E [11/Mar/2017:12:19:29 -0500] Unknown browse protocol "CUPS" ignored.
The man pages suggest [All] and [DNSSD] as possible parameters for BrowseLocalProtocols and for Browsing [Yes] and [No] (though the latter did not raise a warning in the error log).
My changes to cupsd.conf:
# Show shared printers on the local network.
Perhaps this could be considered on one of the next upgrades should time permit.