Set `$_SERVER['HTTPS']` in nginx, in the same way as it's done in Apache; this is necessary for example in WordPress, where the `is_ssl` check will otherwise fail (causing a redirect loop if you have `FORCE_SSL_ADMIN` on).

gistfile1.nginxconf

# The best place to put this is your `fastcgi_params` file.

set $_ssl "off";
# We run SSL on ports 443+, not just one port, to get
# around the lack of SNI in clients' browsers; you might
# safely be able to use "$server_port = 443"
if ( $server_port != 80 ) {
	set $_ssl "on";
}

fastcgi_param HTTPS $_ssl;