Setting up SSL for Nginx behind a Load Balancer

Somewhat related:

Since I'm receiving the request on port 80 I need to tell WordPress that the request is really an HTTPS request. I do the following in wp-config.php which works but this should probably be done at the Nginx level

/*
Set $_SERVER variables if the request is being passed from an HTTPS request from the load balancer. Otherwise is_ssl() doesn't work and we get endless redirects
*/
if ( 'https' === $_SERVER['HTTP_X_FORWARDED_PROTO'] ) {
  $_SERVER['HTTPS'] = 'on';
  $_SERVER['SERVER_PORT'] = '443';
}

If I don't do this then is_ssl() returns false and wp-login.php goes into an infinite redirect loop.