I found that there’s a management web service available in the official Microsoft RDS GitHub for managing WVD. I wrote up a blog post about it at https://www.concurrency.com/blog/june-2019/windows-virtual-desktop-management-web-app. You deploy it as an app service in your own subscription and can use it to manage your own WVD tenants. It doesn’t have 100% of features, but it’s a good alternative to PowerShell’ing your way through everything.