The preferred way to manage Titan/Cornerstone with NT authentication is to add entire groups, rather than individual users. By managing at the group level, fewer inquiries will be made into the database, from a lower level. You will notice improved performance and it will be easier to configure and maintain your server. Some customers even choose to create groups on their Domain that correspond to user classes in Titan/Cornerstone. You could create a new Domain group called "Titan Users" or "Cornerstone Users" which contains any domain users you wish to grant access to the server.