Set parent window handle based on GCM_MODAL_PARENTHWD

Wire up the parent window handle to system prompts and UI helpers.

src/shared/Microsoft.Git.CredentialManager/CommandContext.cs

@@ -109,6 +109,9 @@ public CommandContext()
             Settings          = new Settings(Environment, Git, repoPath);
             HttpClientFactory = new HttpClientFactory(Trace, Settings, Streams);
             IsDesktopSession  = PlatformUtils.IsDesktopSession();
+
+            // Set the parent window handle/ID
+            SystemPrompts.ParentWindowId = Settings.ParentWindowId;
         }
 
         #region ICommandContext

src/shared/Microsoft.Git.CredentialManager/Constants.cs

@@ -47,6 +47,7 @@ public static class EnvironmentVariables
             public const string GcmHttpProxy       = "GCM_HTTP_PROXY";
             public const string GitSslNoVerify     = "GIT_SSL_NO_VERIFY";
             public const string GcmInteractive     = "GCM_INTERACTIVE";
+            public const string GcmParentWindow    = "GCM_MODAL_PARENTHWND";
         }
 
         public static class Http

src/shared/Microsoft.Git.CredentialManager/ConvertUtils.cs

@@ -0,0 +1,28 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license.
+using System;
+
+namespace Microsoft.Git.CredentialManager
+{
+    public static class ConvertUtils
+    {
+        public static bool TryToInt32(object value, out int i)
+        {
+            return TryConvert(Convert.ToInt32, value, out i);
+        }
+
+        public static bool TryConvert<T>(Func<object, T> convert, object value, out T @out)
+        {
+            try
+            {
+                @out = convert(value);
+                return true;
+            }
+            catch
+            {
+                @out = default(T);
+                return false;
+            }
+        }
+    }
+}

src/shared/Microsoft.Git.CredentialManager/ISystemPrompts.cs

@@ -3,8 +3,24 @@
 
 namespace Microsoft.Git.CredentialManager
 {
+    /// <summary>
+    /// Represents native system UI prompts.
+    /// </summary>
     public interface ISystemPrompts
     {
+        /// <summary>
+        /// The parent window handle or ID. Used for correctly positioning and parenting system dialogs.
+        /// </summary>
+        /// <remarks>This value is platform specific.</remarks>
+        object ParentWindowId { get; set; }
+
+        /// <summary>
+        /// Show a basic credential prompt using native system UI.
+        /// </summary>
+        /// <param name="resource">The name or URL of the resource to collect credentials for.</param>
+        /// <param name="userName">Optional pre-filled username.</param>
+        /// <param name="credential">The captured basic credential.</param>
+        /// <returns>True if the user completes the dialog, false otherwise.</returns>
         bool ShowCredentialPrompt(string resource, string userName, out ICredential credential);
     }
 }

src/shared/Microsoft.Git.CredentialManager/Interop/MacOS/MacOSSystemPrompts.cs

@@ -5,6 +5,8 @@ namespace Microsoft.Git.CredentialManager.Interop.MacOS
 {
     public class MacOSSystemPrompts : ISystemPrompts
     {
+        public object ParentWindowId { get; set; }
+
         public bool ShowCredentialPrompt(string resource, string userName, out ICredential credential)
         {
             throw new System.NotImplementedException();

src/shared/Microsoft.Git.CredentialManager/Interop/Windows/WindowsSystemPrompts.cs

@@ -9,6 +9,14 @@ namespace Microsoft.Git.CredentialManager.Interop.Windows
 {
     public class WindowsSystemPrompts : ISystemPrompts
     {
+        private IntPtr _parentHwd = IntPtr.Zero;
+
+        public object ParentWindowId
+        {
+            get => _parentHwd.ToString();
+            set => _parentHwd = ConvertUtils.TryToInt32(value, out int ptr) ? new IntPtr(ptr) : IntPtr.Zero;
+        }
+
         public bool ShowCredentialPrompt(string resource, string userName, out ICredential credential)
         {
             EnsureArgument.NotNullOrWhiteSpace(resource, nameof(resource));
@@ -19,7 +27,7 @@ public bool ShowCredentialPrompt(string resource, string userName, out ICredenti
             {
                 BannerArt = IntPtr.Zero,
                 CaptionText = "Git Credential Manager", // TODO: make this a parameter?
-                Parent = IntPtr.Zero, // TODO: get the parent window handle
+                Parent = _parentHwd,
                 MessageText = message,
                 Size = Marshal.SizeOf(typeof(CredUi.CredentialUiInfo))
             };

src/shared/Microsoft.Git.CredentialManager/Settings.cs

@@ -87,6 +87,12 @@ public interface ISettings : IDisposable
         /// <param name="isDeprecatedConfiguration">True if the proxy configuration method is deprecated, false otherwise.</param>
         /// <returns>Proxy setting, or null if not configured.</returns>
         Uri GetProxyConfiguration(out bool isDeprecatedConfiguration);
+
+        /// <summary>
+        /// The parent window handle/ID. Used to correctly position and parent dialogs generated by GCM.
+        /// </summary>
+        /// <remarks>This value is platform specific.</remarks>
+        string ParentWindowId { get; }
     }
 
     public class Settings : ISettings
@@ -271,6 +277,8 @@ bool TryGetUriSetting(string envarName, string section, string property, out Uri
             return null;
         }
 
+        public string ParentWindowId => _environment.Variables.TryGetValue(Constants.EnvironmentVariables.GcmParentWindow, out string parentWindowId) ? parentWindowId : null;
+
         /// <summary>
         /// Try and get the value of a specified setting as specified in the environment and Git configuration,
         /// with the environment taking precedence over Git.

src/shared/TestInfrastructure/Objects/TestSettings.cs

@@ -30,6 +30,8 @@ public class TestSettings : ISettings
 
         public bool IsDeprecatedProxyConfiguration { get; set; }
 
+        public string ParentWindowId { get; set; }
+
         #region ISettings
 
         public string RepositoryPath { get; set; }
@@ -66,6 +68,8 @@ Uri ISettings.GetProxyConfiguration(out bool isDeprecatedConfiguration)
             return ProxyConfiguration;
         }
 
+        string ISettings.ParentWindowId => ParentWindowId;
+
         #endregion
 
         #region IDisposable

src/shared/TestInfrastructure/Objects/TestSystemPrompts.cs

@@ -8,6 +8,8 @@ public class TestSystemPrompts : ISystemPrompts
     {
         public Func<string, string, ICredential> CredentialPrompt { get; set; } = (resource, user) => null;
 
+        public object ParentWindowId { get; set; }
+
         public bool ShowCredentialPrompt(string resource, string userName, out ICredential credential)
         {
             credential = CredentialPrompt(resource, userName);

src/windows/GitHub.Authentication.Helper.Windows/Program.cs

@@ -23,7 +23,8 @@ public static void Main(string[] args)
                 }
                 else
                 {
-                    var prompts = new AuthenticationPrompts(gui);
+                    IntPtr parentHwnd = GetParentWindowHandle();
+                    var prompts = new AuthenticationPrompts(gui, parentHwnd);
                     var resultDict = new Dictionary<string, string>();
 
                     if (!TryGetArgument(args, "--prompt", out string promptType))
@@ -66,6 +67,12 @@ public static void Main(string[] args)
             }
         }
 
+        private static IntPtr GetParentWindowHandle()
+        {
+            string hwndStr = Environment.GetEnvironmentVariable(Constants.EnvironmentVariables.GcmParentWindow);
+            return ConvertUtils.TryToInt32(hwndStr, out int ptr) ? new IntPtr(ptr) : IntPtr.Zero;
+        }
+
         private static bool TryGetArgument(string[] args, string name, out string value)
         {
             for (var i = 0; i < args.Length; i++)