CORS and subdomains - do subdomains matter?
CORS is not allowing subdomains, so you need to specify them in your server configuration.

If you are using NGINX (or you could use it as a proxy and solve your problem) by providing dynamic cors header response


server {

    root /path/to/your/stuff;

    index index.html index.htm;

     set $cors "";

    if ($http_origin ~* (.*\.yoursweetdomain.com)) {
        set $cors "true";
    }

    server_name yoursweetdomain.com;

    location / {

        if ($cors = "true") {
            add_header 'Access-Control-Allow-Origin' "$http_origin";
            add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS, DELETE, PUT';
            add_header 'Access-Control-Allow-Credentials' 'true';
            add_header 'Access-Control-Allow-Headers' 'User-Agent,Keep-Alive,Content-Type';
        }


        if ($request_method = OPTIONS) {
            return 204;
        }

    }
}



Source here