Vpn settings per vpn

This CL adds a setting for each VPN
- When no_config_vpn user restriction is applied, user can't change anything in the page
- Launch the subsetting activity in the corresponding user to unlock keystore and force work challenge
- Show dialog when user replace always-on-VPN package
- When forget VPN, unset always-on-vpn

TODO: show per-VPN status in VPN list

Change-Id: Ica360ea44117db6a4ecfaed1eec6c188189c246c

src/com/android/settings/vpn2/VpnUtils.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * 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.
+ */
+package com.android.settings.vpn2;
+
+import android.content.Context;
+import android.net.ConnectivityManager;
+import android.security.Credentials;
+import android.security.KeyStore;
+
+/**
+ * Utility functions for vpn
+ */
+public class VpnUtils {
+
+    public static String getLockdownVpn() {
+        final byte[] value = KeyStore.getInstance().get(Credentials.LOCKDOWN_VPN);
+        return value == null ? null : new String(value);
+    }
+
+    public static void clearLockdownVpn(Context context) {
+        KeyStore.getInstance().delete(Credentials.LOCKDOWN_VPN);
+        // Always notify ConnectivityManager after keystore update
+        context.getSystemService(ConnectivityManager.class).updateLockdownVpn();
+    }
+}