I have an app (Docker Registry) behind haproxy which has a particular protocol it’s clients expect that includes a static header in ALL responses - even 4xx and 5xx.
I can easily add this header to responses within the backend but not to 401 (note: haproxy itself is performing the auth checking).
Just to confirm: is there no way of setting headers on ALL 4xx and and 5xx responses just be adding lines to haproxy.cfg
?