Goal: 

• Having a way to show a human-readable permission list, i.e. a function that returns joined array of permission.
• It would be nice to have a limit for the length of such a human-readable list.

We could create a new struct named Permissions: an array of strings, and have a receiver function that converts it to s string as you described.
type Permissions []string

func (p Permissions) String() string {
return "...."
}
Therefore, we need to change []string to Permissions struct in our code.
Acceptance Criteria:

It is possible to use a function to concat and shorten the missing permission list.

Usage 1: https://github.com/RHEnVision/provisioning-backend/blob/02fc79d184d3cea493b159c06d101da92d538534/cmd/pbackend/statuser.go#L189

Possible usage 2: as an API call, and use it on the frontend: https://issues.redhat.com/browse/HMS-1245