string folderPath = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.DesktopDirectory), "Shared");

            var directory = new DirectoryInfo(Directory.CreateDirectory(folderPath).FullName);
            var directorySecurity = directory.GetAccessControl();
            directorySecurity.SetAccessRuleProtection(true, false);
            directory.SetAccessControl(directorySecurity);

            var sid = new SecurityIdentifier(WellKnownSidType.WorldSid, null);
            var security = directory.GetAccessControl();
            var rule = new FileSystemAccessRule(@"<domain/username>", FileSystemRights.Read, InheritanceFlags.ContainerInherit | InheritanceFlags.ObjectInherit, PropagationFlags.None, AccessControlType.Allow);
            security.AddAccessRule(rule);
            directory.SetAccessControl(security);

            using (ManagementClass managementClass = new ManagementClass("Win32_Share"))
            using (ManagementBaseObject inParams = managementClass.GetMethodParameters("Create"))
            {
                inParams["Description"] = "My Files Share";
                inParams["Name"] = "My Files Share";
                inParams["Path"] = folderPath;
                inParams["Type"] = 0x0;
                using (ManagementBaseObject outParams = managementClass.InvokeMethod("Create", inParams, null))
                {
                    if ((uint)(outParams.Properties["ReturnValue"].Value) != 0)
                    {
                        throw new Exception("Unable to share directory.");
                    }
                }
            }