feature: support git.core.askpass (#239)

src/Views/Askpass.axaml.cs

@@ -0,0 +1,52 @@
+using System;
+
+using Avalonia.Input;
+using Avalonia.Interactivity;
+
+namespace SourceGit.Views
+{
+    public partial class Askpass : ChromelessWindow
+    {
+        public string KeyName
+        {
+            get;
+            private set;
+        } = string.Empty;
+
+        public string Passphrase
+        {
+            get;
+            set;
+        } = string.Empty;
+
+        public Askpass()
+        {
+            DataContext = this;
+            InitializeComponent();
+        }
+
+        public Askpass(string keyname)
+        {
+            KeyName = keyname;
+            DataContext = this;
+            InitializeComponent();
+        }
+
+        private void BeginMoveWindow(object sender, PointerPressedEventArgs e)
+        {
+            BeginMoveDrag(e);
+        }
+
+        private void CloseWindow(object sender, RoutedEventArgs e)
+        {
+            Console.Out.WriteLine("No passphrase entered.");
+            Environment.Exit(-1);
+        }
+
+        private void EnterPassword(object sender, RoutedEventArgs e)
+        {
+            Console.Out.Write($"{Passphrase}\n");
+            Environment.Exit(0);
+        }
+    }
+}