Is your feature request related to a problem? Please describe.
At my office we perform some pre-config on accounts using OCC on our NextCloud server.
It is possible to create calendars for users using OCC, but not to create shares for these calendars.

Describe the solution you'd like
It would be nice to include the 3 following commands:

• dav:list-shares user
• dav:set-share user calendar target user|group 1|0
• dav:delete-share user calendar target user|group

Describe alternatives you've considered
So far I do have coded these functions against the latest version (20.0.0). It works as expected on my local instance of NextCloud.
But:

• I'm not familiar with the code and structure of NextCloud/Calendar so a review may be necessary
• I'm not familiar at all with git/github devel process, so I don't know at this stage how to make a proper "patch proposal"

I added the 3 commands files (mostly inspired by other existing commands in apps/dav/lib/Command/). Please let me know if it of any interest for the project and what I can do to participate the right way if needed.

commands.zip