Stripe PHP - 如何使用现有客户/卡创建令牌

I've seen many similar posts, but cannot find one that answers my question. I am able to retrieve an existing customer and their cards, but cannot figure out how to create a token using this. All the examples I find require card info (e.g. card number cvv etc...), which if you retrieve a card through the API I don't have access to. I'm sure it's something simple I'm missing:

$customer = \Stripe\Customer::retrieve($customer_id);
$card = $customer->sources->retrieve($card_id);

$token = \Stripe\Token::create(array(
      "card" => // What to put here???
    )
  );

As @zico explained in a comment, you don't need to create new tokens once you've saved the card with a customer object. You can simply pass the customer's ID in the customer parameter, and optionally the card's ID in the source parameter (if the customer has multiple cards and you want to charge a non-default card).

$charge = \Stripe\Charge::create(array(
    "amount" => 400,
    "currency" => "usd",
    "customer" => "cus_...", // ID of the customer you want to charge
    "source" => "card_...", // ID of the specific card, only needed if the customer has
                            // multiple cards and you want to charge a different
                            // card than the default one
));