Set admin users for demo hub

[yuvipanda]

Since we want everyone to be able to sign up, we don't set
allowed_users.

Fixes #421

[consideRatio]

Hmmm the changes suggested only adds an admins section, not anything about removing allowed_users. How then could it fix #421?

This is an example for the spelman hub that would cause the observed issue.

              allowed_users: &spelman_users
                - [email protected]
                - [email protected]
                - [email protected]
                - [email protected]
                - [email protected]
                - [email protected]
                - [email protected]
              admin_users: *spelman_users

[yuvipanda]

@consideRatio ah, because when I filed #421 I was setting both allowed_users and admin_users. For spelman and other hubs, we want the admins to explicitly add other users who should be allowed to login (see docs). So by config we'll only allow admin users to log in - everyone else is manually entered in the hub admin interface. The demo hub is different.

[consideRatio]

Btw, shouldn't admin users always have access? I wonder if something like this could work?

              # explicitly set to an empty list to disallow access to anyone but the admin users
              allowed_users: []
              admin_users:
                - user1
                - user2

Hmmm probably not, the traitlet is a Set, so I assume it defaults to a blank set and blank set is what we would get by explicitly setting the allowed_users to []. See https://github.com/jupyterhub/jupyterhub/blob/6be3160d7487bb362df7095f24454ef2814951fc/jupyterhub/auth.py#L109-L122

[damianavila]

Btw, shouldn't admin users always have access?

I was saying the same in a previous conversation with @GeorgianaElena: #395 (comment)