This is plainly a bug, but apparently fixing bugs is a feature request around here according to support.
When trying to add an internet radio station that requires authentication by GET parameter, e.g. https://listen.di.fm/premium_high/trance.pls?listen_key=af68e74fd0ea01xxxxxx (I have removed a few characters of the key) Roon does not appear to be able to find a radio station at the address.
The returned .pls from the source looks like this:
Title1=DI.FM - Trance
Title2=DI.FM - Trance
Title3=DI.FM - Trance
I suspect - though without slapping a HTTPS proxy in the way, can’t confirm - that Roon is ignoring the GET parameter and just making a request for the .pls file with no parameters.
Roon should correctly handle a standard URI that contains parameters - if all it does is transparently follow the URI then it would work.