Auth redirect and custom URI protocol handlers

[mlynch]

How should apps using stable Windows App SDK release channels handle authentication redirects that have to open a link with a Custom URI handler so the app can handle them and complete the authentication flow? I found this for UWP apps but it seems to require some additional event handler methods on Application that aren't available in WindowsAppSDK: https://learn.microsoft.com/en-us/windows/uwp/launch-resume/handle-uri-activation

[mlynch]

I was able to make some progress on this, for anyone else who struggles with this in the future. First, you need to implement single app instancing, because it doesn't make sense to the user if they get redirected back to your app and it launches a new instance. Second, you can handle the URI that launches the app and you can do that solely through the APIs available today in Windows App SDK. The trick is you need to override the Main method and implement instancing.

The system is pretty complex, so I basically followed this sample but changed the File launch type stuff to Protocol: https://github.com/microsoft/WindowsAppSDK-Samples/blob/main/Samples/AppLifecycle/Instancing/cs-winui-packaged/CsWinUiDesktopInstancing/CsWinUiDesktopInstancing/Program.cs. Additionally, the sample is weirdly written such that it launches individual windows depending on the name of the file you open, which makes no sense. Cut all that out and change the instancing key to be a single string, and then make sure to bind the Activated event handler when the first launch happens.

Here's a repo that handles the protocol and only ever opens a single window: https://github.com/mlynch/windowsappsdk-instancing