diff --git a/contrib/fwupd.spec.in b/contrib/fwupd.spec.in
index b011292b1b8..42ea2024a88 100644
--- a/contrib/fwupd.spec.in
+++ b/contrib/fwupd.spec.in
@@ -326,6 +326,9 @@ for fn in /etc/fwupd/remotes.d/*.conf; do
     fi
 done
 
+# ensure this is private
+chmod 0660 /etc/fwupd/redfish.conf
+
 %preun
 %systemd_preun fwupd.service
 
diff --git a/libfwupdplugin/fu-plugin.c b/libfwupdplugin/fu-plugin.c
index 9744af9d608..b431f6d4187 100644
--- a/libfwupdplugin/fu-plugin.c
+++ b/libfwupdplugin/fu-plugin.c
@@ -9,6 +9,7 @@
 #include "config.h"
 
 #include <errno.h>
+#include <fcntl.h>
 #include <fwupd.h>
 #include <glib/gstdio.h>
 #include <gmodule.h>
@@ -2417,6 +2418,46 @@ fu_plugin_set_config_value(FuPlugin *self, const gchar *key, const gchar *value,
 	return g_key_file_save_to_file(keyfile, conf_path, error);
 }
 
+#if !GLIB_CHECK_VERSION(2, 66, 0)
+
+#define G_FILE_SET_CONTENTS_CONSISTENT 0
+typedef guint GFileSetContentsFlags;
+static gboolean
+g_file_set_contents_full(const gchar *filename,
+			 const gchar *contents,
+			 gssize length,
+			 GFileSetContentsFlags flags,
+			 int mode,
+			 GError **error)
+{
+	gint fd;
+	gssize wrote;
+
+	if (length < 0)
+		length = strlen(contents);
+	fd = g_open(filename, O_CREAT, mode);
+	if (fd <= 0) {
+		g_set_error(error,
+			    G_IO_ERROR,
+			    G_IO_ERROR_FAILED,
+			    "could not open %s file",
+			    filename);
+		return FALSE;
+	}
+	wrote = write(fd, contents, length);
+	if (wrote != length) {
+		g_set_error(error,
+			    G_IO_ERROR,
+			    G_IO_ERROR_FAILED,
+			    "did not write %s file",
+			    filename);
+		g_close(fd, NULL);
+		return FALSE;
+	}
+	return g_close(fd, error);
+}
+#endif
+
 /**
  * fu_plugin_set_secure_config_value:
  * @self: a #FuPlugin
@@ -2438,7 +2479,8 @@ fu_plugin_set_secure_config_value(FuPlugin *self,
 				  GError **error)
 {
 	g_autofree gchar *conf_path = fu_plugin_get_config_filename(self);
-	gint ret;
+	g_autofree gchar *data = NULL;
+	g_autoptr(GKeyFile) keyfile = g_key_file_new();
 
 	g_return_val_if_fail(FU_IS_PLUGIN(self), FALSE);
 	g_return_val_if_fail(error == NULL || *error == NULL, FALSE);
@@ -2447,17 +2489,18 @@ fu_plugin_set_secure_config_value(FuPlugin *self,
 		g_set_error(error, FWUPD_ERROR, FWUPD_ERROR_NOT_FOUND, "%s is missing", conf_path);
 		return FALSE;
 	}
-	ret = g_chmod(conf_path, 0660);
-	if (ret == -1) {
-		g_set_error(error,
-			    FWUPD_ERROR,
-			    FWUPD_ERROR_INTERNAL,
-			    "failed to set permissions on %s",
-			    conf_path);
+	if (!g_key_file_load_from_file(keyfile, conf_path, G_KEY_FILE_KEEP_COMMENTS, error))
 		return FALSE;
-	}
-
-	return fu_plugin_set_config_value(self, key, value, error);
+	g_key_file_set_string(keyfile, fu_plugin_get_name(self), key, value);
+	data = g_key_file_to_data(keyfile, NULL, error);
+	if (data == NULL)
+		return FALSE;
+	return g_file_set_contents_full(conf_path,
+					data,
+					-1,
+					G_FILE_SET_CONTENTS_CONSISTENT,
+					0660,
+					error);
 }
 
 /**
diff --git a/libfwupdplugin/fu-self-test.c b/libfwupdplugin/fu-self-test.c
index 2dbc9c94ff8..aaf49c172b1 100644
--- a/libfwupdplugin/fu-self-test.c
+++ b/libfwupdplugin/fu-self-test.c
@@ -674,6 +674,62 @@ _plugin_device_added_cb(FuPlugin *plugin, FuDevice *device, gpointer user_data)
 	fu_test_loop_quit();
 }
 
+static void
+fu_plugin_config_func(void)
+{
+	GStatBuf statbuf = {0};
+	gboolean ret;
+	gint rc;
+	g_autofree gchar *conf_dir = NULL;
+	g_autofree gchar *conf_file = NULL;
+	g_autofree gchar *fn = NULL;
+	g_autofree gchar *testdatadir = NULL;
+	g_autofree gchar *value = NULL;
+	g_autoptr(FuPlugin) plugin = fu_plugin_new(NULL);
+	g_autoptr(GError) error = NULL;
+
+	/* this is a build file */
+	testdatadir = g_test_build_filename(G_TEST_BUILT, "tests", NULL);
+	(void)g_setenv("FWUPD_SYSCONFDIR", testdatadir, TRUE);
+	conf_dir = fu_path_from_kind(FU_PATH_KIND_SYSCONFDIR_PKG);
+
+	/* remove existing file */
+	fu_plugin_set_name(plugin, "test");
+	conf_file = g_strdup_printf("%s.conf", fu_plugin_get_name(plugin));
+	fn = g_build_filename(conf_dir, conf_file, NULL);
+	ret = fu_path_mkdir_parent(fn, &error);
+	g_assert_no_error(error);
+	g_assert_true(ret);
+	g_remove(fn);
+	ret = g_file_set_contents(fn, "", -1, &error);
+	g_assert_no_error(error);
+	g_assert_true(ret);
+
+	/* set a value */
+	ret = fu_plugin_set_config_value(plugin, "Key", "True", &error);
+	g_assert_no_error(error);
+	g_assert_true(ret);
+	g_assert_true(g_file_test(fn, G_FILE_TEST_EXISTS));
+
+	/* check it is world readable */
+	rc = g_stat(fn, &statbuf);
+	g_assert_cmpint(rc, ==, 0);
+	g_assert_cmpint(statbuf.st_mode & 0777, ==, 0644);
+
+	/* read back the value */
+	value = fu_plugin_get_config_value(plugin, "Key");
+	g_assert_cmpstr(value, ==, "True");
+	g_assert_true(fu_plugin_get_config_value_boolean(plugin, "Key"));
+
+	/* check it is private, i.e. only readable by the user/group */
+	ret = fu_plugin_set_secure_config_value(plugin, "Key", "False", &error);
+	g_assert_no_error(error);
+	g_assert_true(ret);
+	rc = g_stat(fn, &statbuf);
+	g_assert_cmpint(rc, ==, 0);
+	g_assert_cmpint(statbuf.st_mode & 0777, ==, 0640);
+}
+
 static void
 fu_plugin_devices_func(void)
 {
@@ -3598,6 +3654,7 @@ main(int argc, char **argv)
 	g_test_add_func("/fwupd/progress{finish}", fu_progress_finish_func);
 	g_test_add_func("/fwupd/bios-attrs{load}", fu_bios_settings_load_func);
 	g_test_add_func("/fwupd/security-attrs{hsi}", fu_security_attrs_hsi_func);
+	g_test_add_func("/fwupd/plugin{config}", fu_plugin_config_func);
 	g_test_add_func("/fwupd/plugin{devices}", fu_plugin_devices_func);
 	g_test_add_func("/fwupd/plugin{device-inhibit-children}",
 			fu_plugin_device_inhibit_children_func);