scgi_param

Sets a parameter that should be passed to the SCGI server. The value can contain text, variables, and their combination. These directives are inherited from the previous level if and only if there are no scgi_param directives defined on the current level.

Standard CGI environment variables should be provided as SCGI headers, see the scgi_params file provided in the distribution:

location / {
    include scgi_params;
    ...
}

If the directive is specified with if_not_empty (1.1.11) then such a parameter will not be passed to the server until its value is not empty:

scgi_param HTTPS $https if_not_empty;