server {

    listen 443 ssl;
    listen 443 quic;
    http3 on;
    ssl_protocols TLSv1.3;
    add_header Alt-Svc 'h3=":443"; ma=86400' always;

    server_name mas.{YOURDOMAIN.COM};

    ssl_certificate     /etc/letsencrypt/live/mas.{YOURDOMAIN.COM}/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/mas.{YOURDOMAIN.COM}/privkey.pem;

    location / {
        proxy_pass http://127.0.0.1:8881;

        proxy_http_version 1.1;

        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto https;
        proxy_set_header X-Forwarded-Host $host;
    }
}