server {
listen 4440 ssl http2;
server_name tudomino.com;
root /var/www/html/;
ssl_certificate "/certificado.crt";
ssl_certificate_key "/certificado.key";
ssl_session_cache shared:SSL:1m;
ssl_session_timeout 10m;
ssl_ciphers HIGH:!aNULL:!MD5;
ssl_prefer_server_ciphers on;

    location / {
                 proxy_pass http://127.0.0.1:4445;
                 proxy_http_version 1.1;
                 proxy_set_header Upgrade $http_upgrade;
                 proxy_set_header Connection "upgrade";
    }

    error_page 404 /404.html;
        location = /40x.html {
    }

    error_page 500 502 503 504 /50x.html;
        location = /50x.html {
    }

}

map $http_upgrade $connection_upgrade {
default upgrade;
'' close;
}

En el archivo de configuracion de FOP2 usr/local/fop2/fop2.cfg deshabilita el certificado SSL.
listen_ip = 127.0.0.1
listen_port = 4445
sslproxy=1
proxy_port=4440

Con esto debe funcionar haciendo offloading SSL en el nginx cambiando el wss a ws internamente.

Saludos,

Saludos,