为什么 nginx sub_filter 不适用于 proxy_pass？

Question

目标

我想绕过通过反向代理的同源策略，iframe以便对iframe.

问题一

srciframe 的设置为https://example1.com/iframe-app. 但这仍然会在浏览器中引发同源策略违规。所以浏览器仍然会看到 iframe 中的页面，因为它不是源自https://example1.com/，这似乎没问题，因为如果底层页面具有相同的来源，那么它的 ajax 请求将不起作用。

问题二

所以我尝试使用 nginxsub_filter指令将我的 javascript 注入响应 html。但是，没有在响应中添加任何内容。也许这是因为响应是由于 https 协议而加密的？

题

为什么sub_filter不起作用以及如何使其工作？

nginx 配置

server {
    
            root /var/www/example1.com/html;
            index index.html index.htm index.nginx-debian.html;
    
            server_name example1.com www.example1.com;
    
    
            location / {
                    proxy_pass http://localhost:4000;
            }
    
            location /iframe-app {
                    rewrite ^/iframe-app(.*) /$1 break;

                    proxy_pass http://example2.com;
                    
                    proxy_set_header Accept-Encoding "";
                    
                    proxy_redirect off;
                    
                    sub_filter '</head>' '<script>...code</script></head>';
                    sub_filter_once on;
                    sub_filter_types text/html;
    
            }
    
    
        listen [::]:443 ssl ipv6only=on; # managed by Certbot
        listen 443 ssl; # managed by Certbot
        ssl_certificate /etc/letsencrypt/live/example1.com/fullchain.pem; # managed by Certbot
        ssl_certificate_key /etc/letsencrypt/live/example1.com/privkey.pem; # managed by Certbot
        include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
        ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot
    
    
    server {
        if ($host = www.example1.com) {
            return 301 https://$host$request_uri;
        } # managed by Certbot
    
    
        if ($host = example1.com) {
            return 301 https://$host$request_uri;
        } # managed by Certbot
    
    
            listen 80;
            listen [::]:80;
    
            server_name example1.com www.example1.com;
            return 404; # managed by Certbot
    }