11. restapi: Add authentication filter

This patch adds the authentication filter to the RESTAPI. This doesn't
currently have any effect, as this filter does nothing if the principal
isn't available in the HTTP request. It will have an effect only if at
least one negotiating authenticator is manually configured for the
application

Change-Id: Ie39e0d41bddb4fb5c5ee9d0cc4b46d3fd3c6469b
Signed-off-by: Juan Hernandez <juan.hernandez@redhat.com>
Signed-off-by: Yair Zaslavsky <yzaslavs@redhat.com>