NGNIX Reverse Proxy Setup + Jetty Backend

I have deployed vaadin webapp on jetty container, direct access works fine. 

I have been battling with NGINX reverse proxy setup, but I am always getting session cookie invalid or session invalid error. 

The client and NGINX are configured with SSL. and NGINX and jetty is HTTP.

Client <=> NGINX <=> Jetty

The NGINX conf:

server {
    listen 443;
    ssl    on;
    ssl_certificate /dashboard.io.crt.pem;
    ssl_certificate_key /dashboard.io.key.pem;

    keepalive_timeout 70;
    server_name local.dashboard.io;

    root    /tools/jetty-distribution-9.2.10.v20150310/webapps/dashboard;
    index   index.html;

    location /dashboard/ {
        proxy_set_header X-Forwarded-Host $host;
        proxy_set_header X-Forwared-Server $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header Host $host;

        proxy_pass http://127.0.0.1:8080/dashboard/;

    }
}

I see information on Vaadin deployment topic flying all over the place. 

Can you please give a concrete example of this usecase.

Thanks,
Alan