Setting the following in your community_wsgi.ini file should enable remote authentication in the tool shed. Features like this that are available in Galaxy itself are usually also available in the tool shed (and function the same way) since the code base supporting the features is shared across both applications. Let us know if you bump into problems with this, but please keep all communication on the dev list.
# User authentication can be delegated to an upstream proxy server (usually
# Apache). The upstream proxy should set a REMOTE_USER header in the request.
# Enabling remote user disables regular logins. For more information, see: