Currently no inbuilt support for Azure National Azure clouds (https://docs.microsoft.com/en-us/azure/active-directory/develop/authentication-national-cloud)

Single-Cloud workflows work exactly the same as the Global cloud, but use a different URL as seen in the above linked page.

Multi-cloud workflow is a bit strange, initial authorization calls can be made to the Global Cloud instance (the public onehttps://login.microsoftonline.com) But if you pass instance_aware=true in the code request query string, the response will contain a "cloud_instance_host_name" parameter that will tell you if the request was forwarded to one of the national clouds. At which point future requests for the workflow need to go to that cloud instance's url.

I have patched together a solution for my use-case, but I don't think it would fit with your API structure, so hopefully you can figure out a way to tie it in.