public static void GetAllUsers(ClientContext context)
        {
            Web webs = context.Web;
            var siteUsers = from user in webs.SiteUsers
                            where user.PrincipalType == Microsoft.SharePoint.Client.Utilities.PrincipalType.User
                            select user;
            var usersResult = context.LoadQuery(siteUsers);
            context.ExecuteQuery();
            foreach (var user in usersResult)
            {
                Console.WriteLine(user.LoginName + " - " + user.Email);
            }
        }