Asp.Net OWIN OnAuthenticationFailed

AspNet_OWIN_OnAuthenticationFailed.cs

public void ConfigureAuth(IAppBuilder app)
{
    app.SetDefaultSignInAsAuthenticationType(CookieAuthenticationDefaults.AuthenticationType);

    app.UseCookieAuthentication(new CookieAuthenticationOptions());

    app.UseOpenIdConnectAuthentication(
        new OpenIdConnectAuthenticationOptions
        {
            ResponseType = OpenIdConnectResponseType.CodeIdToken,
            ClientId = clientId,
            Authority = Authority,
           //...

            Notifications = new OpenIdConnectAuthenticationNotifications()
            {
                // If there is a code in the OpenID Connect response, redeem it for an access token
                AuthorizationCodeReceived = (context) =>
                {
                    // ...
                },

                // On Authentication Failed
                AuthenticationFailed = (context) =>
                {
                    String ErrorMessage = context.Exception.Message;
                    String InnerErrorMessage = String.Empty;

                    String RedirectError = String.Format("error_message={0}", ErrorMessage);

                    if (context.Exception.InnerException != null)
                    {
                        InnerErrorMessage = context.Exception.InnerException.Message;
                        RedirectError = String.Format("{0}&inner_error={1}", RedirectError, InnerErrorMessage);
                    }

                    // or you can just throw it
	            // throw new Exception(RedirectError);

                    RedirectError = RedirectError.Replace("\r\n", "  ");

                    context.Response.Redirect("/?" + RedirectError);
                    context.HandleResponse();
                    return Task.FromResult(0);
                }
            }

      });

// ...