Ruby (or your Ruby JSON-RPC library) isn't setting the Authorization: HTTP header from the username:password in the URL.
I don't know anything about Ruby, but Mr. Google might be able to shed some light-- you need to either set the Authorization: header yourself to do the HTTP Basic authentication (I seem to recall some Ruby code on the Wikipedia page about HTTP Basic Authentication) or, in some languages/frameworks there's a way of setting up a 'context' for HTTP connections so the authentication happens properly.