Hi,
I have done some researches and lab tests and found that HTML5 Web Client deployment will must need RD connection broker.
Set up the Remote Desktop web client for your users
https://learn.microsoft.com/en-us/windows-server/remote/remote-desktop-services/clients/remote-desktop-web-client-admin
Remote Desktop HTML5 Web Client on Windows Server
http://woshub.com/rds-html5-web-client/
Thanks,
Eleven