Okay, so I just got a Roku Streaming Stick for my dad, and I wanted to set it up so it could use PLEX, which is what I use to stream everything from my PC.
I was going nuts, because it kept telling me it couldn’t log into the server, because the server was “unauthorized”, even though I let it accept non-secure connections.
The fix, courtesy of gsparx on Reddit, is the following (the following example is if you want to get it to play on devices connected to your home network):
In the PLEX app on your computer, go to Settings -> Server -> Network. There will be a box that says “List of IP addresses and networks that are allowed without authorization”. Enter 192.168.1.0/24 into that box. You may need to refresh, but your Roku should now be able to access your server. You may have to enter a different IP depending on your configuration, but that one worked for me, since, again, I’m using it on my home network.
I hope this helps some people. It was driving me nuts.