ASP.NET with OpenIdAuthentication: redirect to url if not authorized

I am attempting to write an ASP.NET application that uses a hybrid authentication scheme. A user can either have his username and password hash stored in the UserStore, or he can authenticate via Azure Active Directory.

I have created the login form pictured. It has the standard UserName and Password inputs, but also has a "Login via Active Directory" button.

This works well.

Now for the problem: The application's home page has the [Authorize] attribute.

public class DefaultController : Controller
{
    [Authorize]
    public ViewResult Index()
    { 
    // Implementation
    }
}

If the user is not logged in, I want it to redirect to the page Account/Login, allowing the user to choose the authentication method.

Once I added IAppBuilder.UseOpenIdConnectAuthentication to the pipeline setup, it no longer redirects to that page. Instead, it goes straight to the Microsoft Login page.

How do I configure it so that OpenID authentication is part of the system, but allow me to specify how to perform redirections when the user is not authenticated?

Here's the code where I set up the pipeline:

appBuilder.SetDefaultSignInAsAuthticationType(CookieAuthenticationDefaults.AuthenticationType_;
var cookieAuthenticationOptions = new CookieAuthenticationOptions
{
     AuthenticationType = DefaultAuthenticationType.ApplicationCookie,
     LoginPath = new Microsoft.Owin.PathString("/Account/Login"),
     Provider = new Security.CookieAuthenticationProvider()
};
appBuilder.UseCookieAuthentication(cookieAuthenticationOptions);
// Now the OpenId authentication
var notificationHandlers = new OpenIdConnectAuthenticationNotificationHandlers 
{
   AuthorizationCodeReceived = async(context) => {
       var jwtSecurityToken = context.JwtSecurityToken;
       // I've written a static method to convert the claims
       // to a user
       var user = await GetOrCreateUser(context.OwinContext, jwtSecurityToken.Claims);
       var signInManager = context.OwinContext.Get<SignInManager>();
       await signInManager.SignInAsync(user, true, false);
   }
}
var openIdOptions = new OpenIdConnectAuthenticationOptions
{
     ClientId = "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxx",
     Authority = "https://login.microsoftonline.com/xxxxx.onmicrosoft.com",
     PostLogoutRedirectUri = "https://localhost:52538/Account/Login",
     Notifications = notifcationHandlers
}
appBuilder.UseOpenIdConnectAuthentication(openIdOptions);

When you click "Active Directory Signin", it posts to "Account/SignInWithOpenId"

public ActionResult SignInWithOpenId()
{
    // Send an OpenID Connect sign-in request.
    if (!Request.IsAuthenticated)
    {
        var authenticationProperties = new AuthenticationProperties
        {
            RedirectUri = "/"
        };
        HttpContext.GetOwinContext().Authentication.Challenge
        (
            authenticationProperties,
            OpenIdConnectAuthenticationDefaults.AuthenticationType
        );
        return new EmptyResult();
    }
    else
    {
        return RedirectToAction("Index", "Default");
    }
}

The call to IAppBuilder.UseOpenIdConnectAuthentication(...) puts an Owin middleware component in the pipeline. When ASP.NET MVC returns an HttpResponse of 401 (Unauthorized), the Owin Middleware component detects this and changes it to an Http Redirect (code 302), and the redirection path is to the Open Id provider.

But there's a way to get around this: before the middleware component performs the redirect, it invokes the callback RedirectToIdentityProvider. From here, you can override this redirection.

Here is my code that overrides the redirection unless it is from the request path Account/SignInWithOpenId.

var notificationHandlers = new OpenIdConnectAuthenticationNotifications
{
    AuthorizationCodeReceived = async(context) => {
       // Sign in the user here
    },
    RedirectToIdentityProvider = (context) => {
        if(context.OwinContext.Request.Path.Value != "/Account/SignInWithOpenId")
        {
             context.OwinContext.Response.Redirect("/Account/Login");
             context.HandleResponse();
        }
        return Task.FromResult(0);
    }
}
var openIdOptions = new OpenIdConnectAuthenticationOptions
{
     ClientId = "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxx",
     Authority = "https://login.microsoftonline.com/xxxxx.onmicrosoft.com",
     PostLogoutRedirectUri = "https://localhost:52538/Account/Login",
     Notifications = notifcationHandlers
}
appBuilder.UseOpenIdConnectAuthentication(openIdOptions);