[Catalyst] Preventing simultaneous logins

[Daniel McBrearty]

>>
>> 1. checking whether there is an existing session associated this username
>
> Session::PerUser ?
>

I looked briefly at this, but I'm a bit wary because
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?