Try the Ubuntu docs instead of the Debian docs. They're more up to date.
invalid csrf token in NodeBB 0.7.x
when I try to login I got Forbidden page and my console said below message.
1/6 17:48  - error: /login
invalid csrf token
that bugs happen only a few day later when It installed.
how can I fix that
The same for me here after a fresh install (nodejs is behing nginx-ssl + varnish). It has worked once. After I've got this error
I've found the issue. The problem was coming from the varnish's configuration, which was playing the set-cookie value.