Credential FRP: Add ACTION_CONFIRM_FRP_CREDENTIAL to ConfirmCredential

Bug: 36814845
Test: adb shell settings put global device_provisioned 0 && adb shell am start -a android.app.action.CONFIRM_FRP_CREDENTIAL
Change-Id: Id6ce6bc5ebd9c9e2a88790cc800678aff50e580f

src/com/android/settings/Utils.java

@@ -1012,7 +1012,24 @@ public final class Utils extends com.android.settingslib.Utils {
             return getCredentialOwnerUserId(context);
         }
         int userId = bundle.getInt(Intent.EXTRA_USER_ID, UserHandle.myUserId());
-        return enforceSameOwner(context, userId);
+        if (userId == LockPatternUtils.USER_FRP) {
+            return enforceSystemUser(context, userId);
+        } else {
+            return enforceSameOwner(context, userId);
+        }
+    }
+
+    /**
+     * Returns the given user id if the current user is the system user.
+     *
+     * @throws SecurityException if the current user is not the system user.
+     */
+    public static int enforceSystemUser(Context context, int userId) {
+        if (UserHandle.myUserId() == UserHandle.USER_SYSTEM) {
+            return userId;
+        }
+        throw new SecurityException("Given user id " + userId + " must only be used from "
+                + "USER_SYSTEM, but current user is " + UserHandle.myUserId());
     }
 
     /**