What I know about the NNTP protocol can fit in a thimble, but it seems the NNTP server software would have to first support such a login. I don't remember seeing an SSL option in my newsreader software, although there is a "Login w/ Secure Password Authentication" option. A quick look over the Net::NNTP docs did not find any mentions to a secure authentication method, so I think you might be out of luck.
One possible option (if you have a login on the news server) is to use stunnel or ssh to port forward the NNTP port, which would then be a secure connection. YYMV.