On infra.nasqueron.org, a browser refresh was needed to update the log,
ctrl + shift + r for example. Yet, headers are configured not to cache it.
If headers are specified in both location and if block, the more precise
block wins (here the if):
"There could be several add_header directives. These directives are
inherited from the previous configuration level if and only if there
are no add_header directives defined on the current level."
We then need a more precise configuration with every headers.
Reference: http://nginx.org/en/docs/http/ngx_http_headers_module.html