Single login through magpie

[mishaschwartz]

Right now, a user who wants to use jupyterhub in a PAVICS node has to log in separately in jupyterhub. This queries magpie so the user data doesn't have to exist in two places but it is still unnecessary to require a user to potentially log in twice.

Instead we should have a single login location (through magpie) and have jupyterhub accept the logged in user through a request header. This can be achieved by using an authenticator like the one described here (https://github.com/cwaldbieser/jhub_remote_user_authenticator) as well setting the Authenticator.auto_login variable.

Optional: do the same thing for other services that provide logins (eg: geoserver)

[mishaschwartz]

This is being implemented in Ouranosinc/Magpie#589 which uses tokens passed through oauth protocols to give users access to protected resources on nodes other than the one they have an account on.