X-Sendfile:

X-Sendfile:

[1] mod_proxy_scgi - Apache HTTP Server Version 2.4 ( 版) <http://httpd.apache.org/docs/current/en/mod/mod_proxy_scgi.html#ProxySCGISendfile>

The gateway looks for a backend response header called X-Sendfile and interprets the value as the filename to serve. The header is removed from the final response headers.