On client side, each user will have to run a signed program named “Setup-ConnectionClient.exe” as a pre-requisite
This program is available on your server, in the RDPlus program folder: C:\Program Files (x86)\RDPlus\Clients\WindowsClient:

It is also available in C:\Program Files (x86)\RDPlus\Clients\www\ConnectionClient, so your users can just run the program once on your web server address: http://xxxxxxxxxxx/ConnectionClient/Setup-ConnectionClient.exe