User Authentication

[hoo761]

Currently users are "signed in" without any authentication. They just give their git username and are able to comment as that user. This can be a problem because any person can use anyone's git username to show up as that person.

Authentication with GitHub or another service will make sure that the person who is commenting or creating threads is actually that person.

[hoo761]

This will help pave the road for #23 by linking to an external API to help with notifications and mentions.

[ktaletsk]

Another idea could be linking the username with the JupyterHub id when running through JupyterHub