[codex] Handle CredWrite logon session failures

src/Exceptions/KeyStorageException.cs

@@ -0,0 +1,17 @@
+using System;
+
+namespace KeePassWinHello
+{
+    [Serializable]
+    public class KeyStorageException : KeePassWinHelloException
+    {
+        public override bool IsPresentable { get { return true; } }
+
+        public KeyStorageException(string message) : base(message) { }
+        public KeyStorageException(string message, Exception inner) : base(message, inner) { }
+        protected KeyStorageException() { }
+        protected KeyStorageException(
+          System.Runtime.Serialization.SerializationInfo info,
+          System.Runtime.Serialization.StreamingContext context) : base(info, context) { }
+    }
+}

src/KeePassWinHello.csproj

@@ -61,6 +61,7 @@
     <Compile Include="Exceptions\AuthProviderInvalidKeyException.cs" />
     <Compile Include="Exceptions\AuthProviderSystemErrorException.cs" />
     <Compile Include="Exceptions\AuthProviderException.cs" />
+    <Compile Include="Exceptions\KeyStorageException.cs" />
     <Compile Include="AuthProviders\IAuthProvider.cs" />
     <Compile Include="AuthProviders\UIContext.cs" />
     <Compile Include="AuthProviders\WinHelloProviderForegroundDecorator.cs" />
@@ -124,4 +125,4 @@
     <Message Importance="normal" Text="Copy artifacts to KeePass plugins directory." />
     <Exec ContinueOnError="true" Command="powershell.exe -NoProfile -NonInteractive -ExecutionPolicy Bypass -File &quot;$(ProjectDir)..\Deploy-Plugin.ps1&quot; -ForDebug -Verbose" WorkingDirectory="$(ProjectDir).." />
   </Target>
-</Project>
+</Project>

src/KeyManagement/KeyManager.cs

@@ -198,6 +198,10 @@ private void Lock(bool isDbLocking, string dbPath, CompositeKey databaseMasterKe
             {
                 // it's OK
             }
+            catch (KeyStorageException ex)
+            {
+                _uiContextManager.CurrentContext.ShowError(ex);
+            }
         }
 
         public void RevokeAll()

src/KeyManagement/Storage/KeyWindowsStorage.cs

@@ -11,6 +11,7 @@ internal class KeyWindowsStorage : IKeyStorage
     {
         #region Credential Manager API
         private const int ERROR_NOT_FOUND = 0x490;
+        private const int ERROR_NO_SUCH_LOGON_SESSION = 0x520;
 
         private const int CRED_TYPE_GENERIC = 0x1;
 
@@ -96,7 +97,7 @@ public void AddOrUpdate(string dbPath, ProtectedKey protectedKey)
                     Marshal.Copy(data, 0, ncred.CredentialBlob, data.Length);
                     ncred.CredentialBlobSize = (uint)data.Length;
 
-                    CredWrite(ref ncred, 0).ThrowOnError("CredWrite");
+                    WriteCredential(ref ncred);
                 }
                 finally
                 {
@@ -111,6 +112,38 @@ public void AddOrUpdate(string dbPath, ProtectedKey protectedKey)
             }
         }
 
+        private static void WriteCredential(ref CREDENTIAL credential)
+        {
+            if (CredWrite(ref credential, 0).Result)
+                return;
+
+            int errorCode = Marshal.GetLastWin32Error();
+            if (errorCode == ERROR_NO_SUCH_LOGON_SESSION)
+                throw new KeyStorageException(GetNoLogonSessionMessage());
+
+            throw new EnviromentErrorException("CredWrite", errorCode);
+        }
+
+        private static string GetNoLogonSessionMessage()
+        {
+            string message = "Windows Credential Manager cannot save the database key because Windows reported that the current logon session is not available. The database key was not saved persistently.";
+            if (IsCurrentProcessElevatedSafe())
+                message += " This can happen when KeePass is running as Administrator; restart KeePass without elevation to use Credential Manager storage.";
+            return message;
+        }
+
+        private static bool IsCurrentProcessElevatedSafe()
+        {
+            try
+            {
+                return UAC.IsCurrentProcessElevated;
+            }
+            catch
+            {
+                return false;
+            }
+        }
+
         public bool ContainsKey(string dbPath)
         {
             IntPtr ncredPtr = IntPtr.Zero;