elpa & proxy authentication

[Luca Ferrari]

Hi,
I believe this is trivial but I cannot find a solution: I'm behind an
http proxy that requires authentication, and I cannot install packages
using elpa.
I've placed in my .emacs file something like:

(setq url-proxy-services '(("no_proxy" . "work\\\\.com")
                           ("http" . "<user>:<password>@<proxy>:<port>")))

and the first time I try to refresh the package list I got prompted
for the username, that is the same I specified, and for the password,
and then a generic error "unable to download package gnu" appears.
Then I try to download and install a package, I'm prompted again for
username and password for the proxy (and this time the username is the
one I'm running emacs within, not the one specified in the
configuration file) and Emacs still gives me an error that cannot
download: "Error during download request: proxy authentication
required".

Any idea?
Thanks,
Luca