stripe api checking for existing card - php

Question

I'm sure I'm missing something obvious here, but I can't get my head around how to check for an existing card against a customer.
I'm using the stripe connect api within an laravel app to manage payments on behalf of others, and the basic process is as follows:
a stripe token is created via stripe.js and submitted with the payment form
if the customer exists in the local database, I grab their stripe_id, otherwise a new customer is created using the token as the source/card
a charge is then created using the retrieved or new customer stripe_id
Currently, if the customer returns and uses a different card, as the charge only includes a customer, not source, it'll be charged against their default card regardless.
What I'd like to do is:
create a stripe token
check customer against local database etc
check card fingerprint against customer's cards
if necessary, create new card on customer's record
create charge using both customer and card ids
Simply put: I can't see where in the process a persistent card_id is generated; both those used in the stripe.js response, and when created in the stripe dashboard, appear to be unique, meaning every charge creates a brand-new card object in stripe.
I know I can retrieve a list of cards stored against a customer's account - but where do I get the initial card_id from to search against?
I've seen a question that touches on this here - Can I check whether stripe a card is already existed before going to create new one? - but I don't know Ruby, so can't make head nor tail of it.
EDIT:
Simpler version - is there a way to get the fingerprint as described in the stripe docs here - https://stripe.com/docs/api/php#card_object - without having to first create a card object ?

Answer 1

So the idea here would be to use the fingerprint on the Card object or the Token object and not the id itself as those would be different if you add the same card multiple times.
When you get a new card token you can retrieve it through the Retrieve Token API and look for the fingerprint in the card hash.
You would keep a list of known fingerprints in your database associated with a specific customer and/or card so that you can detect duplicate cards.
NOTE: make sure you are using the secret keys to get those information. otherwise if you are using the publishable key, you might not get the fingerprint value.

Answer 2

I created a function to do this:
$customer is the stripe customer object
$stripe_account is either your account's stripe ID or the connected account's stripe ID
$token comes from stripe.js elements
$check_exp allows you to decide if you want to check the card's expiration date as well, because the fingerprint does not change if the card's number is the same
stripe PHP API 7.0.0
function check_duplicate_card($customer, $stripe_account, $token, $check_exp) {
$loc = "check_duplicate_card >> ";
$debug = true;
if ($debug) {
// see here for an explanation for logging: http://php.net/set_error_handler >> Examples
trigger_error("$loc started", E_USER_NOTICE);
}
try
{
// get token data
$response = \Stripe\Token::retrieve(
$token,
["stripe_account" => $stripe_account]
);
$token_fingerprint = $response->card->fingerprint;
$token_exp_month = $response->card->exp_month;
$token_exp_year = $response->card->exp_year;
if ($debug) {
trigger_error("$loc token_fingerprint = $token_fingerprint; token_exp_month = $token_exp_month; token_exp_year = $token_exp_year", E_USER_NOTICE);
}
// check for duplicate source
if ($debug) {
trigger_error("$loc customer sources = " . json_encode($customer->sources), E_USER_NOTICE);
}
$duplicate_found = false;
foreach ($customer->sources->data as &$value) {
// get data
$fingerprint = $value->fingerprint;
$exp_month = $value->exp_month;
$exp_year = $value->exp_year;
if ($fingerprint == $token_fingerprint) {
if ($check_exp) {
if (($exp_month == $token_exp_month) && ($exp_year == $token_exp_year)) {
$duplicate_found = true;
break;
}
} else {
$duplicate_found = true;
break;
}
}
}
if ($debug) {
trigger_error("$loc duplicate_found = " . json_encode($duplicate_found), E_USER_NOTICE);
}
} catch (Exception $e) {
if ($e instanceof \Stripe\Exception\ApiErrorException) {
$return_array = [
"status" => $e->getHttpStatus(),
"type" => $e->getError()->type,
"code" => $e->getError()->code,
"param" => $e->getError()->param,
"message" => $e->getError()->message,
];
$return_str = json_encode($return_array);
trigger_error("$loc $return_str", E_USER_WARNING);
http_response_code($e->getHttpStatus());
echo $return_str;
} else {
$return_array = [
"message" => $e->getMessage(),
];
$return_str = json_encode($return_array);
trigger_error("$loc $return_str", E_USER_ERROR);
http_response_code(500); // Internal Server Error
echo $return_str;
}
}
if ($debug) {
trigger_error("$loc ended", E_USER_NOTICE);
}
return $duplicate_found;
}