IdentityModel.OidcClient library doesn't seem to work with UWP - .net-core

Question

We are using ASP.NET Identity with IdentityServer4. We've added a Client to use with Azure AD. This works great within a web page, that part is working.
Our end goal is a UWP app, so we found the IdentityModel.OidcClient which has a UWP sample. This sample has two browser classes. We configured HTTPS, but the WabBrowser class now refuses to connect to the site at all. If I change the config to hit https://demo.identityserver.io then it works, but all the other config is the same, so I'm not sure what the problem could be. It shows an error message in the pop up browser that it could not connect.
I looked at the SystemBrowser class, but this logs in fine, then the browser window does not close, and even if we close it, the code doesn't move on to get back a result. Looking at the source, this is not surprising, it calls:
Launcher.LaunchUriAsync(new Uri(options.StartUrl));
and that's all. The RedirectUri is not passed in, and mechanism appears to exist to use it. So, the behaviour we see appears to be the extent of what the class can do.
Looking at the console .NET Core sample, it has a SystemBrowser class that works. I updated the UWP sample to use the Fall Creators Update and was able to bring in the ASP.NET Core dlls needed to compile this code. It sets up a class like this:
public LoopbackHttpListener(int port, string path = null)
{
path = path ?? String.Empty;
if (path.StartsWith("/")) path = path.Substring(1);
_url = $"http://127.0.0.1:{port}/{path}";
_host = new WebHostBuilder()
.UseKestrel()
.UseUrls(_url)
.Configure(Configure)
.Build();
_host.Start();
}
and I can confirm this gets called only once, but even if I hard code an unused IP address, I get an error that the IP is in use.
So, at this stage, the sample that exists for UWP works for the demo server but not for ours (I suspect an HTTPS issue, but that's not the error I get), and importing code that works for a Core sample, does not work either. I've spent a couple of days on this and would appreciate a nudge in the right direction.
So, to recap, the WabBrowser seems the best bet but, for my localhost IdentityServer I get this:
and if I try to use a .NET Core library that works elsewhere, it thinks a port is in use. I suspect I need to work out why WabBrowser can't connect to my local site. I have turned off Fiddler. I can browse to my https URL and get a disco document, in the browser, at https://localhost:44305/.well-known/openid-configuration.

Answer 1

There are extra steps necessary to enable localhost in the Web Authentication Broker -
https://msdn.microsoft.com/en-us/library/windows/desktop/jj658959%28v=vs.85%29.aspx?f=255&MSPPError=-2147217396

Answer 2

This website gave me the fix. Here is a synopsis:
Remove loopback isolation
For security and reliability reasons, UWP applications are not allowed to send requests to the loopback interface. While Visual Studio automatically creates exemptions for debugged apps, this feature won't be helpful in this case, as the authentication broker always executes in a separate process.
If you see this (cryptic) error message in your Windows event logs, then you're likely facing this issue:
AuthHost encountered a navigation error at URL: [...] with StatusCode: 0x800C0005.
One option to fix it is to use the loopack exemption utility developed by Eric Lawrence. It's natively included in Fiddler 4 but can also be downloaded as a standalone software. To allow the authentication broker to communicate with the loopback interface, exempt the applications starting with microsoft.windows.authhost and save your changes:
If everything was properly configured, you should now see the login/consent page returned by your server.