我可以在nginx上游使用http和https吗

我有如下Nginx配置:

upstream staging {
    server myappstaging.somedomain.com;
}

upstream prod {
    server myapp.somedomain.com:443;
}

# map to different upstream backends based on header
map $http_x_server_select $pool {
    default "prod";
    staging "staging";
}

server {
    listen 80;
    server_name myapp.mydomain.com;

    location / {
        proxy_pass https://$pool;
    }
}

我想把请求转发给 x-server-select http://myappstaging.somedomain.com 为了刺激 https://myapp.somedomain.com:443

Nginx有可能做到这一点吗?