chunked_transfer_encoding off;
add_header Content-Length $sent_http_content_length;

http {
    ...
    proxy_temp_path  /var/cache/nginx/proxy_temp 1 2;
    proxy_cache_path  /var/cache/nginx/proxy_cache levels=1:2 keys_zone=static:100m inactive=60m max_size=1g;
    ...
    server {
        ...
        location ~* ^/app/.*\.(css|eot|gif|jpg|js|ico|pdf|png|svg|ttf|woff|woff2)$ {
            proxy_cache static;
            proxy_cache_key $request_method$request_uri;
            proxy_cache_convert_head off;
            proxy_cache_use_stale error timeout invalid_header updating http_500 http_502 http_503 http_504;
            proxy_cache_background_update on;
            proxy_cache_revalidate on;
            proxy_cache_valid 200 301 302 5m;
            proxy_cache_valid 404 1m;
            ...
        }
        ...
    }
}