Media Server :: RTMP & Flash Media Streaming Server Live Application?

I'm running Flash Media Streaming Server and have only been serving VOD up until now.  I had my network administrator open up port 1935 to the outside world during the setup process and now I can't remember if that was actually required for streaming VOD to clients.  Most documentation I've read says that this port should be open, but I seem to recall reading something at one point that suggested it wasn't necessary.

I've just started messing around with publishing live streams using Flash Media Live Encoder to the Flash Media Streaming Server.  I have that working without issue but was surprised to find that no authentication is required before a client running the live encoder can publish a stream to the Flash Media Streaming Server.  An authentication module is available however it only works with Flash Media Interactive Server and Flash Media Development Server.

If I leave port 1935 open to the outside world, there would be nothing to stop anybody anywhere from streaming video via my server.  Anyone else running a default install of Flash Media Streaming Server and with port 1935 open to the outside should see that this is true of their setup as well.  I'm wondering if I can safely close port 1935 without limiting the functionality of the server or if there's some way I can require authentication prior to publishing a live stream even though I'm not on the four-and-a-half-times-more-expensive edition of the product.