Some Nginx proxy users reported that adding the following block directive is an effective workaround for addressing the missing CORS headers issue.

Please replace XXXX with your actual Confluence domain name:

location ~* \.(eot|ttf|woff|woff2)$ {
    add_header Access-Control-Allow-Origin "https://confluence.XXXX.com";
    try_files $uri @jira;
  }
  location / {
    try_files $uri @jira;
  }
  
  location @jira {
    proxy_pass http://localhost:8080 ;
    proxy_read_timeout 180s;
    proxy_http_version 1.1;
    proxy_redirect off;
  }
CODE