public async Task <IActionResult> Ntlm(string returnUrl = null)
        {
            if (this.User.Identity.IsAuthenticated == false)
            {
                var defaultProperties = new AuthenticationProperties()
                {
                    RedirectUri = returnUrl
                };

                var authContext = new Http.Features.Authentication.AuthenticateContext(ActiveDirectoryOptions.DefaultAuthenticationScheme);
                await HttpContext.Authentication.AuthenticateAsync(authContext);

                if (!authContext.Accepted || authContext.Principal == null)
                {
                    return(new UnauthorizedResult());
                }
            }

            if (string.IsNullOrWhiteSpace(returnUrl))
            {
                return(new OkResult());
            }
            else
            {
                return(Redirect(returnUrl));
            }
        }
        public async Task<IActionResult> Ntlm(string returnUrl = null)
        {
            if (this.User.Identity.IsAuthenticated == false)
            {
                var defaultProperties = new AuthenticationProperties() { RedirectUri = returnUrl };

                var authContext = new Http.Features.Authentication.AuthenticateContext(ActiveDirectoryOptions.DefaultAuthenticationScheme);
                await HttpContext.Authentication.AuthenticateAsync(authContext);

                if (!authContext.Accepted || authContext.Principal == null)
                {
                    return new UnauthorizedResult();
                }
            }

            if (string.IsNullOrWhiteSpace(returnUrl))
                return new OkResult();
            else
                return Redirect(returnUrl);
        }