Duplicate customers appear in Stripe with no subscription

Here is what is happening:

1. The user fills out the account setup step of the subscription form
2. This triggers a customer creation in Stripe
3. The user abandons the checkout and comes back
4. The user fills out the account setup step again, which creates a new customer in Stripe. They then complete the payment, which attaches the subscription to the most recently created Stripe customer.

It's a little confusing, but due to Stripe's new SCA regulations that is how it the data needs to flow. As long as the subscriber in Leaky Paywall has the same Stripe customer id as the one with the Stripe subscription, everything will run smoothly with renewals.