delay oath progressbar visibility

lib/oath/views/oath_screen.dart

@@ -20,6 +20,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_gen/gen_l10n/app_localizations.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:yubico_authenticator/widgets/delayed_visibility.dart';
 
 import '../../app/message.dart';
 import '../../app/models.dart';
@@ -42,6 +43,7 @@ import 'unlock_form.dart';
 
 class OathScreen extends ConsumerWidget {
   final DevicePath devicePath;
+
   const OathScreen(this.devicePath, {super.key});
 
   @override
@@ -210,7 +212,10 @@ class _UnlockedViewState extends ConsumerState<_UnlockedView> {
                   );
                 },
               )
-            : const CircularProgressIndicator(),
+            : const DelayedVisibility(
+                delay: Duration(milliseconds: 200),
+                child: CircularProgressIndicator(),
+              ),
       ),
     );
   }

lib/widgets/delayed_visibility.dart

@@ -0,0 +1,66 @@
+/*
+ * Copyright (C) 2022 Yubico.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import 'dart:async';
+
+import 'package:flutter/material.dart';
+
+class DelayedVisibility extends StatefulWidget {
+  final Duration delay;
+  final Widget child;
+
+  /// Makes child visible after delay
+  const DelayedVisibility(
+      {super.key, required this.delay, required this.child});
+
+  @override
+  State<StatefulWidget> createState() => _DelayedVisibilityState();
+}
+
+class _DelayedVisibilityState extends State<DelayedVisibility> {
+  bool _visible = false;
+  Timer? _timer;
+
+  @override
+  void initState() {
+    super.initState();
+    _timer = Timer.periodic(widget.delay, (timer) {
+      if (mounted) {
+        setState(() {
+          _visible = true;
+        });
+      }
+      timer.cancel();
+      _timer = null;
+    });
+  }
+
+  @override
+  void dispose() {
+    super.dispose();
+    _timer?.cancel();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Visibility(
+      visible: _visible,
+      maintainState: true,
+      maintainAnimation: true,
+      child: widget.child,
+    );
+  }
+}