Make Session Handler more extension friendly

[urg]

We need to extend the session handler to run a few checks and this change will allow us to extend without needing to fork/duplicate code.

[snc]

Is this still needed or do you already use 2.x-dev?

[urg]

I don't have access to that repo anymore (left the company), so not sure if its still in use. @c-cooperjones might know?

[Seldaek]

Closing as this is super old and most likely outdated.