add_header 'Access-Control-Allow-Origin' '*';
add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Content-Range,Range';
add_header 'Access-Control-Expose-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Content-Range,Range';

if ($request_method = 'OPTIONS') {
   add_header 'Access-Control-Max-Age' 1728000;
   add_header 'Content-Type' 'text/plain; charset=utf-8';
   add_header 'Content-Length' 0;
   return 204;
}

index index.html