Based on the compatible list, AuthPoint is not compatible with Windows 2008 R2 and older and can be use on Windows 2012 R2 and later.
Can it be use on Windows 2012?
Windows Server 2012 was released previous to 2012 R2, so it is not supported.
WatchGuard Customer Support
"not supported" in this case doesn't mean that it is guaranteed to not work - it may or may not.
If it doesn't work, then too bad, WG won't fix it.
For unsupported OS versions, WG will not test the latest version of products on them to make sure that they work.
While this recent statement from WG is for WSM, expect the same for AuthPoint etc.
Supported Operating Systems for WSMhttps://www.watchguard.com/wgrd-blog/supported-operating-systems-wsm