Additional payment method

[KBbitsP]

• The plugin now allows adding payment method to existing customers.
• Integration test for the above

[Copilot]

Pull request overview

This PR extends the Stripe payment plugin to support adding an additional payment method to an already-mapped Stripe customer, and introduces an integration test validating the “second payment method” flow.

Changes:

• Update addPaymentMethod to attach PaymentMethods / Tokens / Sources to an existing Stripe customer when a STRIPE_CUSTOMER_ID mapping already exists.
• Add an integration test ensuring a second Stripe PaymentMethod gets attached to the original customer and is persisted locally.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
src/main/java/org/killbill/billing/plugin/stripe/StripePaymentPluginApi.java	Attach newly-added payment methods to an existing Stripe customer instead of always creating a new customer.
src/test/java/org/killbill/billing/plugin/stripe/TestStripePaymentPluginApi.java	Add integration test covering adding a second PaymentMethod to an existing customer/account.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

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[Copilot]

The comment says to call the instance .update() method, but the code actually calls customer.getSources().create(...). Also, the indentation here includes tab characters, which is inconsistent with the surrounding file’s spacing and makes diffs harder to read. Please update the comment to match the behavior and replace tabs with spaces.

[Copilot]

This comment line is mis-indented relative to the surrounding block (it appears to have fewer leading spaces than the adjacent assertions), which makes the test harder to scan. Align it with the other lines in the method.

Suggested change

	// Also verify it's specifically the source we attached, not just any source
	// Also verify it's specifically the source we attached, not just any source

[Copilot]

In the token branch for an existing Stripe customer, calling customer.update with the source param will replace the customer’s default_source in Stripe (i.e., it makes the newly-added card the default). If the intent of addPaymentMethod is to add an additional method without changing defaults (especially when setDefault is false), consider attaching via customer.getSources().create(...) (like the source branch) or otherwise preserving/restoring the previous default source.

Suggested change

	Customer customer = Customer.retrieve(existingCustomerId, requestOptions);
	ImmutableMap<String, Object> updateParams = ImmutableMap.of("source", stripeToken.getId());
	final Customer updatedCustomer = customer.update(updateParams, requestOptions);
	// Use the update response directly — defaultSource is already populated,
	// no need for an extra Customer.retrieve() round-trip
	stripeId = updatedCustomer.getDefaultSource() != null
	? updatedCustomer.getDefaultSource()
	: getTokenInnerId(stripeToken);
	}
	final Map<String, Object> expandParams = new HashMap<>();
	expandParams.put("expand", ImmutableList.of("sources"));
	final Customer customer = Customer.retrieve(existingCustomerId, expandParams, requestOptions);
	final Map<String, Object> attachParams = new HashMap<>();
	attachParams.put("source", stripeToken.getId());
	final PaymentSource sourceForAdditionalData = customer.getSources().create(attachParams, requestOptions);
	stripeId = sourceForAdditionalData.getId();
	}

[Copilot]

This source branch recreates an expandParams map for expand: ["sources"], but the class already has expandSourcesParams for this exact purpose. Reusing expandSourcesParams would avoid duplication and keep the expansion behavior consistent across branches.

Suggested change

	final Map<String, Object> expandParams = new HashMap<>();
	expandParams.put("expand", ImmutableList.of("sources"));
	final Customer customer = Customer.retrieve(existingCustomerId, expandParams, requestOptions);
	final Customer customer = Customer.retrieve(existingCustomerId, expandSourcesParams, requestOptions);