Save custom field via plugin

How do you save a user custom field in PHP ? Easy as that!
$user = Craft::$app->getUser()->getIdentity();
$user->setFieldValues([
'customField' => 1,
]);
Craft::$app->getElements()->saveElement($user);
$user = Craft::$app->getUser()->getIdentity();
$user->setFieldValues([
'customField' => 1,
]);
Craft::$app->getElements()->saveElement($user);