ACL (Access Control List) in DDD (with CQS)

Model

namespace UserManagement.Model
{
    namespace Query
    {
        using System;
        using System.Collections.Generic;

        public class User
        {
            /// <summary>
            ///     Gets the permissions the user has for objects.
            /// </summary>
            public IEnumerable<Tuple<Object, Permission>> Associations { get; private set; }

            public IEnumerable<Group> Groups { get; private set; }

            public string Name { get; set; }
        }

        public class Permission
        {
            /// <summary>
            ///     Gets the users that this permission has for objects.
            /// </summary>
            public IEnumerable<Tuple<Object, User>> Associations { get; private set; }

            public string Name { get; set; }
        }

        public class Group
        {
            public string Name { get; set; }

            /// <summary>
            ///     Gets the users that belong to this group.
            /// </summary>
            public IEnumerable<User> Users { get; private set; }
        }

        public class Object
        {
            /// <summary>
            ///     Gets the permission that users have for this objects.
            /// </summary>
            public IEnumerable<Tuple<Permission, User>> Associations { get; private set; }

            public string Name { get; set; }
        }

        public interface IRepository
        {
            Group GetGroup(string groupName);
            Object GetObject(string objectName);
            Permission GetPermission(string permissionName);
            User GetUser(string userName);
        }
    }

    namespace Command
    {
        using System.Collections.Generic;

        public interface IRepository
        {
            void AddGroup(string groupName, IDictionary<string, object> metadata = null);
            void AddObject(string objectName, IDictionary<string, object> metadata = null);
            void AddPermission(string permissionName, IDictionary<string, object> metadata = null);
            void AddUser(string userName, IDictionary<string, object> metadata = null);
            void RemoveGroup(string groupName);
            void RemoveObject(string objectName);
            void RemovePermission(string permissionName);
            void RemoveUser(string userName);
        }

        public interface IAssociator
        {
            void AddUserToGroup(string userName, string groupName);
            void AssociatePermissionWidthGroup(string permissionName, string objectName, string groupName);
            void AssociatePermissionWithUser(string permissionName, string objectName, string userName);
            void DeassociatePermissionFromGroup(string permissionName, string objectName, string groupName);
            void DeassociatePermissionFromUser(string permissionName, string objectName, string userName);
            void RemoveUserFromGroup(string userName, string groupName);
        }
    }
}