Without knowing the steaming format, html5 vs flash vs ...., it is hard to give an answer.
It might be possible, once your are logged in, to copy the video link and open it in VLC or mplayer. Depending on which multimedia player you are using, a web search will tell you have to start the stream. There are also Firefox plugins for VLC and mplayer.
https://www.techwalla.com/articles/h...gin-in-firefox
Edit: Concurrently posted w/ jggimi. If it is digitally signed/encrypted wi HDCP, you have a challenge. My search did find a wikileaks pdf on how NSA cracked an HDCP video and played it back in mplayer.