Add bugfix desc

Docker-DCO-1.1-Signed-off-by: Mangled Deutz <olivier@webitup.fr> (github: dmp42)
Change standalone header when in mirroring mode (prevents client from sending basic auth headers and overwriting token)

Docker-DCO-1.1-Signed-off-by: Joffrey F <joffrey@docker.com> (github: dmp42)