only show links to services users have access to

[marcwit]

Proposal to improve the display of services in users hub home page by using filters.

While the visibility of services can currently be enabled or disabled by the display value in the jupyterhub_config.py file, there is no fine-grained control of visibility for individual users/groups or the like.
The proposed code changes are intended to address this by introducing the display_filters attribute in the above mentioned file and corresponding adjustments in base.py.
display_filters is currently a Dict() with the keys usernames, groups and roles to filter by. It should be noted that the eventual service will only be displayed if all filters match the respective user.
To implement the filtering, the function get_accessible_services(self, user) in base.py was extended by corresponding lines that (a) read the roles and group membership of the user and (b) perform the filtering and, if the attributes match, add the service to the accessible_services list as usual.
To read the groups and roles, roles.py and user.py have been extended with the respective function/method get_role_names_for(orm_object) and get_groups(self).

In our use case, we want to filter the display of a service based on a group membership, since it is necessary to show the service for certain users and hide it for others.

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[minrk]

Nice! This makes sense. Before I get into detailed review, I have one question: if we filtered based on the appropriate access:services permission, would that suffice (i.e. only show users services they have access to)? Then you wouldn't have two separate collections - visibility and access, you would just have the one - access (which we already have), and visibility is limited to when the link is going to work.

What do you think?

[marcwit]

That's a good suggestion. I have adapted it to that effect. It looks cleaner and clearer that way.

Is that all right?

[minrk]

Thanks! I tidied up the check a little bit and added a test, but this looks great!

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