Set User permission for REST API

On calling REST API using a superuser API KEY to fetch list of all users,
getting the following response :

{
“error”: {
“code”: 401,
“message”: “Unauthorized: You are not allowed to read list of users”
},
“debug”: {
“source”: “api_users.class.php:73 at call stage”,
“stages”: {
“success”: [
“get”,
“route”,
“negotiate”,
“authenticate”,
“validate”
],
“failure”: [
“call”,
“message”
]
}
}
}

This is related to a permission : DolibarrApiAccess::$user->rights->user->user->lire

How to set this permission? Since I am using a superuser API KEY, all user permissions are granted by default.
Please help.