RDGatewayFedAuth.msi accepted token formats?

I'm working on configuring a token server interface for remote desktop gateway. I found an example around using RDGatewayFedAuth.msi from https://learn.microsoft.com/en-us/azure/devtest-labs/configure-lab-remote-desktop-gateway however I am unable to find any documentation on the plugin.

Would anyone be able to share documentation on the plugin (or even better, a source repo)? I am specifically looking for what kind of validation is performed on the token, if other values can be passed through, etc. It would be a lot easier to use something already written instead of trying to write my own from scratch.

Any assistance would be appreciated.