sessions: load all sessions for user

[abraithwaite]

sessions: load all sessions for user

[abraithwaite]

This definitely makes sense. If you want to instrument your app to be able to clear all sessions for an individual user that seems like the only way to do it short of building your own tooling to interact with your store.

I'll add it!

[abraithwaite]

I went ahead and implemented this, however I would like to note that if you wish to revoke all active sessions for a single user, it's only necessary to delete their key in the store.

However, I still believe this is a useful method to have to build tooling with, despite leaking some details about how we're storing them on the backend.