Write Nextcloud groups as CATEGORIES of system address book contacts

[ChristophWurst]

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Is your feature request related to a problem? Please describe.

Nextcloud 27 exposes the system address book with read-only contacts for all system users. It's common to have Nextcloud groups for departments, teams and projects.

Describe the solution you'd like

Add a CATEGORIES property to the system contacts based on the display names of a user's Nextcloud groups.

This requires users to be allowed to see other user's groups.

Describe alternatives you've considered

N/a

Additional context

#19575

[ChristophWurst]

This requires users to be allowed to see other user's groups.

Users do see their own groups at the personal settings / profile settings page (bottom left). If other users should see this information is to be researched or defined.

Right now you can find out the members of a group by adding them to a share or a Talk room. But you can't do the inverse of getting the groups of a user.

[ChristophWurst]

@AndyScherzinger @DaphneMuller @jancborchardt @juliushaertl @nickvergessen @sorbaugh @tobiasKaminsky please excuse the ping-all but this change is worked on in #40997 and I believe we should have platform-wide consent about the exposure of group membership of other users.

Right now you can only see your own groups in the personal settings. You do not see who's member of the admins or any other Nextcloud groups.

If groups are stored with system address book contacts, this information will be visible to all other users for the first time.

Do we want that?

[nickvergessen]

You do not see who's member of the admins

Admins is like the only exception because it's exposed by various apps, including the default shipped data_request
https://github.com/nextcloud/privacy/blob/master/src/components/Admins.vue#L25

But yeah, not sure we should leak all groups.

[tobiasKaminsky]

I am sure that we should not do this, as this is sensitive data.
I remember stories about competing departements in one giant company, where they are not allowed to talk to each other. So imagine one can now see at which projects/groups the others work.

[tcitworld]

I've disabled the feature by default through an appconfig, and there's also other appconfig options to include or exclude groups that will be exposed. What do you think?

[ChristophWurst]

I think that is a good compromise. Groups aren't exposed by default and if admins are okay with exposure they can configure it explicitly.

In the long run groups could have a visibility setting similar to user profile properties. Admins could use them to set the visibility scope of a group:

• Private (default): groups is only visible to admins and members
• Local: only visible to people on the instance. This means we can store it in the system address book but remove the data when sent to another instance
• Federated: visible to everyone on the instance, and also on federated instances. This means we can store it in the system address book and send the data to other instances too.
• Published: visible to everyone. This means we can store it in the system address book and send the data to other instances and the lookup server.

[nickvergessen]

I would even like a "hidden" visibility scope where only admins see the group but not "normal members"