Running Policy Server, and protecting a resource with "Authentication Scheme Type: RADIUS Server Template", how to configure it to use an HTML Form to collect the username and password instead of a basic authentication prompt?
This is not possible in the out of the box Policy Server.
It's only possible when adding the GD Module "XauthRadius" module to the Policy Server. With this module, the Basic Authentication and the HTML Form authentication schemes are available (1).
Consult the Support Matrix to understand the version and OS combination required (2) for the XauthRadius module.