idempotency_key option persisted since v3.4.1

[jurriaan]

We just noticed that some of our payments were failing due to the fact that the same idempotency key was used as in the invoice creation request.

Traced the issue back to this commit:
80d85a5#diff-56800b7863b39756b91e3c43ffed3f51R19
Where the idempotency key was added to the OPTS_KEYS_TO_PERSIST array.

This bug can be triggered with the following code:

invoice = Stripe::Invoice.create(
  { customer: 'cus_foo' },
  { idempotency_key: 'someidempotencykey' }
)
invoice.pay(source: ideal_source.id)

Where before v3.4.1 it will succeed, and after this version it will raise the following error:

Keys for idempotent requests can only be used for the same endpoint they were first used for ('/v1/invoices/in_foobarbaz/pay' vs '/v1/invoices'). Try using a key other than 'someidempotencykey' if you meant to execute a different request. (Stripe::InvalidRequestError)

It seems to me that this change of the OPTS_KEYS_TO_PERSIST is unwanted, since you don't want to reuse the previously used idempotency_key for different requests.

cc @brandur @brandur-stripe

[ob-stripe]

Hey @jurriaan, thanks for the report. I'll let @brandur-stripe take a closer look, but at first glance I think your assessment is correct and the idempotency key should not be persisted.

[brandur-stripe]

Sorry about the trouble here, and thanks for reporting. I've proposed a patch in #599.

Hm, I wonder if it might be worth adding something to stripe-mock so that it would've caught this problem. i.e. A check for recently re-used idempotency keys.

[brandur-stripe]

Fixed released as part of 3.5.3.