I'm not really seeing a lot of documentation but I have implemented external authentication and external providers. But what's missing for me is:
My own research has lead to this:
https://www.identityserver.com/articles/identityserver4-ws-federation-and-sharepoint/ https://github.com/IdentityServer/IdentityServer4.WsFederation Identity Server v3 as Federation Gateway only
Let me know, thanks.
Okay, from my own discoveries and searches for answers, I'm coming to find out that federation gateway is a type of system architecture used to hide and shield how connections are made to external providers. This is true to identity server 4. Identity server can act as a client to these external providers.
if you need to implement that specification with identity server 4, you will need to code your own plug-in to communicate over that protocol. Luckily, Scott Brady (link above) showed us a way to accomplish that. If you're using identity server 3, the team made their own plugin for you to grab from NUGET.
More information later as I get through this. Wish me luck.