what is idmsa.apple.com

IDMSA (full name idmsa.apple.com) is the name of the guard shack placed at the conceptual network security fence built around Apple and Apple services, and you will have to present your identification badge and your secret passcode to the guard to be permitted access within parts of the fenced perimeter at Apple. IDMSA is what you authenticate to.

In more technical jargon, IDMSA a cryptic acronym used as the collective name of the group of computer servers — computers larger, faster, and with more resources and with capabilities necessary for handling the billions of network connections that can be happening — used to provide authentication services for controlling and accessing Apple apps and services. That includes the authentication services used to allow (or to deny) access into the Apple Support Communities.

Much like the network host names you may have assigned to your own local computers and to printers and other devices in your network, or the network host names that have been automatically generated and assigned, idmsa.apple.com is a network host name. Your firewall on your own network might not have a host name assigned by you, but the authentication-related part of the (immense) Apple firewall and authentication services implementation does have a host name, and that name is IDMSA.