HTTPS header missing from single server

[Grant]

>> How can I make nginx set the HTTPS header in a single http/https
>> server?
>
> What is "the HTTPS header"?

I meant to say HTTPS environment variable.

>> piwik with force_ssl=1 on apache goes into a redirect loop
>> because it doesn't know SSL is on due to the nginx reverse proxy.
>
> This sounds like one or more fastcgi_param key/value pairs are not set
> the way your application wants them to be set.
>
> http://nginx.org/r/fastcgi_param is how you set them. And it
> includes an example with the $https variable, which is described in
> http://nginx.org/en/docs/http/ngx_http_core_module.html#variables

I should have mentioned that I'm using proxy_pass.  I was able to get
it working like this:

proxy_set_header X-Forwarded-Proto $scheme;

- Grant