[Globus] Support custom username handling

[NickolausDS]

Move the code responsible for fetching the username to a separate get_username() method so it can be overridden.

An example is running a Globus Jupyterhub Server that can accept logins from one or more providers (Google, ORCID, Any university in CILogon, etc.), wants needs to ensure usernames are unique. That way, person@uchicago.edu and person@gmail.com are assigned different usernames. The jupyterhub config could look like this:

import base64

class OmniProviderOAuthenticator(LocalGlobusOAuthenticator):
    def get_username(self, user_info):
        username, domain = user_info.get('preferred_username').split('@', 1)
        # 'sub' is a uniquely generated uuid by Globus for each user identity
        enc_sub = base64.b32encode(bytes(user_info['sub'], 'utf-8')).decode('utf-8')
        return f'{username}-{enc_sub}'[:32]

c.JupyterHub.authenticator_class = OmniProviderOAuthenticator

This is similar to the GenericOAuthenticator username picker, except the key in Globus will never change, so a callable is always preferred.

[GeorgianaElena]

Thanks @NickolausDS 🎉

[NickolausDS]

Thank you!