uwsgi_param

Sets a parameter that should be passed to the uwsgi 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 uwsgi_param directives defined on the current level.

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

location / {
    include uwsgi_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:

uwsgi_param HTTPS $https if_not_empty;