How to handle cancel button of windows authentication pop-up in asp.net core mvc deployed on Kestrel? - authentication

Question

I'm trying to implement mixed authentication windows + cookie based in asp.net core mvc application. When windows authentication is canceled I want to redirect user to fallback page where can choose windows or cookie based authentication. The app will be deployed on Kestrel not IIS. I'm using .net core 3.1.
Basically I need to redirect user on fallback page when http status code is 401 and substatus code is 1 or 2.
So far I tried to use status code pages as fallows:
In Startup.cs I added
app.UseStatusCodePagesWithReExecute("/Error/Status", "?statusCode={0}");
In ErrorController.cs
public IActionResult Status(int statusCode)
{
var statusCodeReExecuteFeature = HttpContext.Features.Get<IStatusCodeReExecuteFeature>();
if (statusCode == 401)
{
return RedirectToAction("Index", "Fallback");
}
var originalURL =
statusCodeReExecuteFeature.OriginalPathBase
+ statusCodeReExecuteFeature.OriginalPath
+ statusCodeReExecuteFeature.OriginalQueryString;
return Redirect(originalURL);
}
This not works because it breaks windows authentication handshake.
I also tried to implement custom error handler and check HttpResponse.StatusCode == 401, but the error controller method is not hit probably because windows authentication is handled by another layer ..

Answer 1

It took me a few days before I almost thought it can't be done. But finally I figured it out.
My problem was when executing External Authentication on Identity Server 4. I couldn't catch the event when the user clicks "Cancel". I got 401 status code for entering Windows Authentication, for clicking "Cancel" and also when clicking "Signin". The solution is the following:
Place this line in Startup.cs in public void Configure(IApplicationBuilder app):
app.UseStatusCodePagesWithReExecute("/external/ErrorPage", "?statusCode={0}");
After that just create a IActionResult function in controller like this:
[HttpGet]
public IActionResult ErrorPage(int? statusCode = null)
{
if (statusCode.HasValue)
{
return View(new SomeViewModel() { ErrorMessage = statusCode.Value.ToString()});
}
return View();
}