Getting started oauth keys/

I have already integrated Keep with my website. The user selects a product, and it is then processed through Stripe. I have a Stripe webhook that triggers and inserts the data into Keep.

Here is the code:

$invoiceId = $app->blankOrder($conID,$inf_description, $date, 0, 0);

$test = $app->addOrderItem($invoiceId, $product_id, 4, (double)($event_json->amount_captured/100), 1, $inf_description, $inf_description);

$app->manualPmt($invoiceId,(double)($event_json->amount_captured/100),$date,‘Stripe’,$event_json->id,false);

How can I integrate OAuth2?