Good day!

How to make this scheme?

Page generating with custom header (for example "X-Custom-Header: somevalue").
How to check if header exists?

for example:

location / {
if (exists "X-Custom-header") {
....
}

...
}

location / [
if ($http_x_custom_header) {
....
}
}

see http://wiki.nginx.org/HttpCoreModule#.24http_HEADER for more information.

Andrejs