nginx: if-modified-since

nginx.conf

location @fallback {
 proxy_pass http://127.0.0.1:8080;
 proxy_redirect http://127.0.0.1:8080 /;
 proxy_set_header Host $host;
 proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
 proxy_set_header X-Forwarded-Proto $scheme;
 proxy_set_header If-Modified-Since $http_if_modified_since;
 access_log off ;
}