class AppUserStore : IUserStore<AppUser>, IUserRoleStore<AppUser>
    {
        // Лишнее убрал...

 
        // Нужные методы
        public Task<AppUser> FindByIdAsync(string userId)
        {
            int intUserID;
            
            if (int.TryParse(userId, out intUserID))
                return User.Where(u => u.ID == intUserID).FirstOrDefaultAsync();

            return Task.FromResult<AppUser>(null);
        }

        public Task<AppUser> FindByNameAsync(string userName)
        {            
            return User.Where(u => u.UserName == userName).FirstOrDefaultAsync();
        }

        public Task<IList<string>> GetRolesAsync(AppUser user)
        {
            IList<string> result = user.Roles.ToArray();
            return Task.FromResult(result);
        }

        public void Dispose()
        { }

        // Ненужные методы
        #region Unused

        #region IUserStore<User, int> Members

        public Task CreateAsync(AppUser user)
        {
            throw new NotImplementedException();
        }

        public Task DeleteAsync(AppUser user)
        {
            throw new NotImplementedException();
        }

        public Task UpdateAsync(AppUser user)
        {
            throw new NotImplementedException();
        }

        #endregion

        #region IUserRoleStore<User, int> Members

        public Task AddToRoleAsync(AppUser user, string roleName)
        {
            throw new NotImplementedException();
        }

        public Task<bool> IsInRoleAsync(AppUser user, string roleName)
        {
            throw new NotImplementedException();
        }

        public Task RemoveFromRoleAsync(AppUser user, string roleName)
        {
            throw new NotImplementedException();
        }

        #endregion

        #endregion
    }

ko.bindingHandlers.validationElement = {
        init: function (element: HTMLElement, valueAccessor: () => any, allBindings: KnockoutAllBindingsAccessor, viewModel, bindingContext: KnockoutBindingContext) {
            ko.utils.domNodeDisposal.addDisposeCallback(element, () => {
                $(element).tooltip("destroy");
            });
        },
        update: function (element: HTMLElement, valueAccessor: () => any, allBindings: KnockoutAllBindingsAccessor, viewModel, bindingContext: KnockoutBindingContext) {
            var value = valueAccessor();

            if (!ko.validation.utils.isValidatable(value))
                return;

            var isValid: boolean = value.isValid();
            var isModified: boolean = value.isModified();
            var isErrorVisible = !isValid; // && isModified;
            var $element = $(element);
            var $formGroup = $element.hasClass("form-group") ? $element : $element.parents(".form-group:first");

            $element.tooltip("destroy");

            if (isErrorVisible) {
                $element.tooltip({
                    title: value.error,
                    placement: "bottom",
                    container: "#validationMessagesTooltipsHolder"
                });

                $formGroup.addClass("has-error");
            } else
                $formGroup.removeClass("has-error");
        }
    };