Return a dict with extra data retrieved from cern oauth.

def fetch_extra_data(resource):
    """Return a dict with extra data retrieved from cern oauth."""
    person_id = resource.get('PersonID', [None])[0]
    identity_class = resource.get('IdentityClass', [None])[0]
    department = resource.get('Department', [None])[0]

    return dict(
        person_id=person_id,
        identity_class=identity_class,
        department=department
    )