how to set upgrade-insecur-requests based on nginx
<p>I have changed my site to <code>https</code>,but I used the cdn of static files in the code. it can't work and the chrome console show the errors like this:</p>

<pre><code>Mixed Content: The page at 'https://a.example.com/static/' was loaded over HTTPS, but requested an insecure stylesheet 'http://cdn.bootcss.com/bootstrap/3.3.5/css/bootstrap.min.css'. This request has been blocked; the content must be served over HTTPS.
</code></pre>

<p>I have add the <code>add_header Content-Security-Policy upgrade-insecure-requests;</code> in the nginx configuration file like this:</p>

<pre><code>server {
    listen 80;
    listen 443;
    server_name a.example.com;
    add_header Content-Security-Policy upgrade-insecure-requests;

    if ($scheme != "https") {
       return 301 https://$server_name$request_uri;
       #rewrite ^ https://$server_name$request_uri? permanent;
    }


    ssl on;
    ssl_certificate /etc/nginx/ssl/example.crt;
    ssl_certificate_key /etc/nginx/ssl/example.key;

    ssl_session_timeout 5m;

    ssl_protocols SSLv3 TLSv1 TLSv1.1 TLSv1.2;
    ssl_ciphers "HIGH:!aNULL:!MD5 or HIGH:!aNULL:!MD5:!3DES";
    ssl_prefer_server_ciphers on;

    gzip on;
    gzip_proxied any;
    gzip_types text/plain application/xml application/json;
    client_max_body_size 8M;
    access_log /var/log/nginx/example.log;
    location / {
            proxy_pass http://10.10.10.110:5000;
            proxy_set_header  X-Real-IP  $remote_addr;
            proxy_set_header Host $host;
    }
    location ^~ /static/ {

            proxy_pass http://10.10.10.110:8888;
            proxy_set_header  X-Real-IP  $remote_addr;
            proxy_set_header Host $host;
           #proxy_set_header Content-Security-Policy upgrade-insecure-requests;
    }
</code></pre>

<p>}</p>

<p>but it does't work yet! Can someone tell me how to fix this? thx :)</p>