App process keeps running after app is closed

[aries-zhang]

Describe the bug

Cross posting this bug here: AzureAD/microsoft-authentication-library-for-dotnet#4967 in case it is relating to WASDK.

We have a WASDK + WinUI 3 + .NET 8 based app which uses MSAL .Net for authentication. We came to notice that after an interactive login (account picker window shown) the app process will not exit after it is closed. With the "Analyze wait chain" option in Task Manager, it shows a svchost process is holding the app process, and this svchost process points to the "TokenBroker" service.

I've managed to reproduce it with the minimum code below. This issue seems to only reproduce when both of the following 2 conditions are met:

1. There is a WebView2 control with a Source property (no matter set via XAML or code-behind).
2. The WAM's interactive login window (account picker) is shown.

<Window
    x:Class="App2.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:App2"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">

    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="80" />
            <RowDefinition />
        </Grid.RowDefinitions>

        <StackPanel Grid.Row="0" HorizontalAlignment="Center" VerticalAlignment="Center" Orientation="Horizontal">
            <Button Click="SignInButton_Click" Content="Sign in" />
        </StackPanel>

        <Grid Grid.Row="1" HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
            <WebView2 x:Name="MyWebView" Source="https://bing.com" />
        </Grid>
    </Grid>
</Window>

private void SignInButton_Click(object sender, RoutedEventArgs e)
{
    if (client == null)
    {
        client = PublicClientApplicationBuilder.Create(clientId: AppId)
            .WithAuthority(authorityUri: "https://login.microsoftonline.com/common")
            .WithBroker(brokerOptions: new BrokerOptions(BrokerOptions.OperatingSystems.Windows))
            .Build();
    }

    IntPtr handle = WinRT.Interop.WindowNative.GetWindowHandle(this);

    DispatcherQueue.TryEnqueue(async () =>
    {
        try
        {
            AcquireTokenInteractiveParameterBuilder tokenBuilder = client.AcquireTokenInteractive(["https://graph.microsoft.com/.default"])
                .WithParentActivityOrWindow(handle)
                .WithUseEmbeddedWebView(false);

            AuthenticationResult result = await tokenBuilder.ExecuteAsync().ConfigureAwait(false);

            Debug.WriteLine("Signed in.");
        }
        catch (MsalException ex) when (ex.ErrorCode == "authentication_canceled")
        {
            Debug.WriteLine($"Sign in canceled.");
        }
        catch (Exception ex)
        {
            Debug.WriteLine($"Sign in failed: {ex.Message}.");
            throw;
        }
    });
}

This issue is really strange since it does not repro when there is not a WebView2 control in the app or the WebView2 control does not have a "Source" property set. I've also noticed with the same code it does not repro on Windows 10 (22H2).

Steps to reproduce the bug

The code is also posted in this repo: aries-zhang/WinUI3-MSAL-Demo. Please follow these steps to reproduce:

1. Clone the code.
2. Build and run the app.
3. The app should show bing.com and a "Sign in" button in the top (now if you close the app, the process shuts down normally).
   
4. Click "Sign in", when account picker pops up, close the account picker window to cancel login (or sign in with an account. It does not matter as long as the sign in window is shown).
5. Close the app.
6. Open Task Manager, search App2.exe in the "Details" tab, the process is still running.
7. Right click App2.exe, select "analyze wait chain", it shows the svchost process.
   
   
8. Search with the svchost process's id, right click, select "go to services", it shows the "TokenBroker" service.
   
   

Expected behavior

App process should shutdown when it is clsoed.

Screenshots

No response

NuGet package version

Windows App SDK 1.6.3: 1.6.241114003

Packaging type

Packaged (MSIX)

Windows version

Windows 11 version 22H2 (22621, 2022 Update)

IDE

Visual Studio 2022

Additional context

No response