前端https请求到A，A将该https请求转发的B

场景： 前端传过来一个https请求到A服务器的Nginx，然后A服务器将该请求以https方式转发到B服务器的Nginx
A服务器配置：

server {
        listen       443;
        server_name  lalala1.com;
        ssl on;
        ssl_certificate /home/zhuhg/ssl/server.crt;
        ssl_certificate_key /home/zhuhg/ssl/server.key;
        ssl_session_timeout 5m;
        ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
        ssl_ciphers ECDHE-RSA-AES128-GCM-SHA256:HIGH:!aNULL:!MD5:!RC4:!DHE;
        ssl_prefer_server_ciphers on;

        #charset koi8-r;

        #access_log  logs/host.access.log  main;

        location / {
            proxy_set_header Host $host;
            proxy_set_header X-Real-IP $remote_addr;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_set_header X-Forwarded-Proto $scheme;
            proxy_redirect http:// $scheme://;
            proxy_pass http://lalala2.com;
            index  index.html index.htm;
        }

这里的$scheme是Nginx内置变量，为进来的请求协议，在这个例子中$scheme==https