I looked briefly at this, but I'm a bit wary because
1. checking whether there is an existing session associated this usernameSession::PerUser ?
C::P::Session::Store::Fastmmap warns against being used with it. What
is PerUser doing that is special in that respect, and what is a good
backend for it?
REading the docs for it, it seems like something slightly different -
keeping the same session in place, even if the user logs in in the
middle of it, if I understand correctly?