SEC-768: Send card details to Stripe in the request body, not the URL

[msuitcase]

Description

ReferralCustomerService.createStripeToken builds the POST https://api.stripe.com/v1/tokens request with card[number], card[exp_month], card[exp_year] and card[cvc] appended to the URL query string. It calls setDoOutput(true) but never writes a body. Query strings are routinely captured by access logs, outbound proxies, APM/tracing tools and Referer headers, so cardholder data could be retained outside the payment path (PCI DSS requirement 3 / 4).

This change writes the same form-encoded string to the connection's output stream and drops it from the URL. Stripe already expects application/x-www-form-urlencoded bodies on this endpoint (it is what easypost-ruby, easypost-go and easypost-csharp do today), so there is no behavioural change for callers. InternalUtilities.getEncodedURL is reused unchanged as the encoder.

Also adds a Next Release CHANGELOG entry.

Tracking: SEC-768 (internal).

Testing

• No Maven on the machine I authored this from, so this has not been compiled here; the change is a new java.io.OutputStream import, one renamed local, and a try-with-resources write. Please run mvn test / checkstyle in CI.
• Cassette re-record needed: src/test/cassettes/referral_customer/referral_add_credit_card.json and create_bad_stripe_token.json were recorded with the card fields in the URL, and TestUtils configures EasyVCR to match byFullUrl().byBody(...), so testReferralAddCreditCard and testCreateBadStripeToken will not replay until re-recorded with the partner / referral prod keys. I do not have those keys. When re-recording, please confirm the recorded URL no longer carries card fields and that the body censor rules cover card[number] and card[cvc].

Pull Request Type

Please select the option(s) that are relevant to this PR.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Improvement (fixing a typo, updating readme, renaming a variable name, etc)

🤖 Generated with Claude Code