CALs are only required for domain user functions, if you're just setting up a filemaker server that users are connecting to without directory level security, then you don't require any CALs at all.
Thanks Mike, that's great news. Of course my MS re-seller tells me differently.
If that was the case, if you installed a web server, you would require a CAL for every user connecting to a hosted website. Same concept for FileMaker. If you’re not running your machine as a domain controller, your FMP users have no need for CALs.
Of course your MS rep was disappointed, they make tons of money on CALs, which is why they can start doing things like giving away their desktop OS updates.
Just to note FileMaker technically works without any CALs as stated at Does FileMaker Server require a Client Access License (CAL)? | FileMaker, you are supposed to have CALs for every user or device accessing a Windows server.
This article from last year clears up some misconceptions Licensing How To: When do I need a Client Access License (CAL)? - Microsoft Volume Licensing Blog - Site Home - TechNet… including that web users need CALs, they don't as Mike points out in most cases, read 5 – Do I need a CAL when my Windows Server is used to run a web server? very closely as it is quite scary depending on your web architecture. Several other questions and answers are quite scary too, like CALs for printers and DHCP.
The TL;DR of that blog is "The general requirement is, any User or Device that accesses the server software, either directly or indirectly, requires a CAL."