Restrict video/audio call start to specific groups #17465

Feature request

Since my English isn't very good, an AI helped me write my message in English.

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

On larger Nextcloud instances (e.g. 200+ users), there is currently no way to restrict who can start video/audio calls without completely disabling the Talk app for those users.

If all users have access to Talk, any user can create a new group conversation and immediately start a video call — including calls with external guests via public links. On a self-hosted server without a High Performance Backend, this can cause significant resource and bandwidth issues, especially if users start using it as a free video conferencing tool outside of the organization.

The only current workaround is to restrict the Talk app to a specific group entirely, which also removes chat functionality for all other users — an unacceptable trade-off in many environments.

Describe the solution you'd like

Add an admin setting that allows restricting the ability to start video or audio calls to specific users or groups, independently of the general Talk app access.

For example:

• A new field in the Talk admin settings: "Groups allowed to start calls"
• If left empty: all users can start calls (current behavior, default)
• If one or more groups are configured: only members of those groups can start calls; all other users can still use Talk for chat and can join calls that were started by an allowed user

This would be analogous to the existing allowed_groups mechanism already used in Talk for other permission scopes.

Describe alternatives you've considered

• Restricting the Talk app to a group: removes chat for everyone else — not acceptable
• Using per-conversation moderator roles: does not prevent users from creating new conversations and starting calls themselves
• Setting default_permissions via occ: controls media permissions within a call, but does not prevent call initiation

Additional context

This feature would be especially valuable for:

• Organizations with many users on self-hosted instances without HPB
• Medical or regulated environments where communication tools must be controlled
• Admins who want to allow broad chat usage while limiting resource-intensive video conferencing to authorized users

The feature should ideally be configurable via both the admin web UI and occ config:app:set.