[Problem/Bug]: WinUI 3 app's process running after window is closed when WebView2 is opened after MSAL .Net interactive login pop up window

[aries-zhang]

What happened?

We have a WinUI 3 (WinAppSDK) + .NET 8 based app which uses MSAL .Net for authentication and WebView2 for the main app content. We noticed that when WebView2 is opened after an MASL 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 an svchost process is holding the app process, and this svchost process points to the "TokenBroker" service, which belongs to "Web Account Manager".

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 MSAL'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;
        }
    });
}

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.
   
   

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).

It does not repro with silent login. It seems to have something to do with MSAL + WebView2 combined. Cross posting here in case it is WebView2 related (also posted in MSAL repo here: AzureAD/microsoft-authentication-library-for-dotnet#4967).

Importance

Moderate. My app's user experience is affected, but still usable.

Runtime Channel

Stable release (WebView2 Runtime)

Runtime Version

No response

SDK Version

No response

Framework

WinUI3/WinAppSDK

Operating System

Windows 11

OS Version

No response

Repro steps

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.
   
   

Repros in Edge Browser

No, issue does not reproduce in the corresponding Edge version

Regression

No, this never worked

Last working version (if regression)

No response

Internal Tracking Number: 57235930