With a $user object, we can verify the user against a permission setting with the can() method. However, how can I retrieve all users who have a specific permission, including those under a group with the permission.
This needs to be generic PHP code as it's located in a service.
I don't think there is a clean or particularly efficient way of doing this using Craft's current services.
It'd have to be something like:
1. Grab all users
2. Loop through them calling craft()->userPermissions->doesUserHavePermission()
3. If true, save user in success array.
Alternatively you could use DbCommand to query the database directly for the info you're looking for.
