Locking a Workplace bot down to specific people can be useful during the testing phase, but also if you only want a sub sector of your organisation to access the bot.
It's really easy to do.
In the integration settings on Workplace you can pick the specific groups.
Warning if using communities you must also select the communities or community that the groups belong to.
Once you've done this, only members of the group can access it. If you are posting a message to a group, you will also need to refresh your groups on the platform.