Implement session ID generation

[drewbryant]

Currently the notebook server is simply using the user's IP address for the session id as stop-gap solution.

This approach works if you assume all users will have unique IP addresses (not necessarily true) and that a user is only working with a single notebook at a time (we want to support working with multiple notebook simultaneously).

Suggestion from nikhilk@

I think something as simple as a JWT encoding of userid + notebookid would be enough. The JWT encoding makes sure you can validate it was this server that generated the session id.

One thing to keep in mind is notebook ids likely change when renaming. In which case, maybe just a JWT encoding of the kernel id?

[drewbryant]

Currently the notebook path is used for selecting the particular session to join. Because a notebook path can change (e.g., on notebook rename), behind the scenes, each session has a unique ID (uuid v4) that is fixed for the duration of the session.

Closing this issue.