SUSE Manager can sync channels from NCC through a corporate proxy.
Channel syncing is done with mgr-ncc-sync. It supports both http/https protocols as well as authentication for proxies.
The easiest way to configure the proxy is by using yast2. mgr-ncc-sync will then read the proxy configuration from yast2's config files. Alternatively, the environment variables HTTP_PROXY and HTTPS_PROXY can be set. Proxy authentication is only supported by setting the username/password in the URL of these environment variables.
We are currently working to fix some issues with some specific proxy server versions. We are also working to allow for setting the proxy authentication credentials through yast2. These fixes will be available in an upcoming maintenance update.