feat: require environmentSubdomain or an explicit useLegacyDomain opt-out

[armando-rodriguez-cko]

Summary

Makes the merchant-specific subdomain (MSSD) mandatory. Callers must now call environmentSubdomain(...), or explicitly opt out with the new, already-@deprecated useLegacyDomain(). Setting both, or neither, throws CheckoutArgumentException at client construction. MSSD is no longer beta and non-MSSD usage will be deprecated, so the previous silent fallback to api.checkout.com had to go.

Changes

• lib/Checkout/AbstractCheckoutSdkBuilder.php — the subdomain is held as a string and the EnvironmentSubdomain is built when the configuration is assembled, so environmentSubdomain() no longer has to be called after environment(); new useLegacyDomain() marked @deprecated; new validateEnvironmentSettings() and requiresEnvironmentSubdomain()
• lib/Checkout/EnvironmentSubdomain.php — createUrlWithSubdomain throws on an invalid subdomain instead of returning the URL unchanged
• lib/Checkout/CheckoutStaticKeysSdkBuilder.php, CheckoutOAuthSdkBuilder.php, Previous/CheckoutStaticKeysPreviousSdkBuilder.php — validate before building, resolve the subdomain through the base class; Previous/ABC exempted
• test/Checkout/Tests/CheckoutDefaultSdkTest.php — covers all four combinations plus an invalid subdomain
• test/Checkout/Tests/TestDomainConfiguration.php (new) + SandboxTestFixture and six integration fixtures — every client the suite builds now chooses a domain

Fixed along the way

environmentSubdomain() used to build the URLs from whatever environment was set at call time, so calling it before environment() silently produced the wrong host.

Verification

900 tests, 0 failures, 246 skipped. phpcs reports 0 errors.

API Reference

• https://api-reference.checkout.com/#section/Base-URLs
• https://www.checkout.com/docs/developer-resources/api/api-endpoints

Breaking changes

Yes, two. This needs a major release, classified and versioned when the release is cut.

1. The merchant-specific subdomain is mandatory for the Default and DefaultOAuth platforms. Code that omitted it and relied on the implicit fallback to api.checkout.com / access.checkout.com now fails at client construction. Migration: set the subdomain, or use the legacy-domain opt-out as a temporary measure. The Previous (ABC) platform is unaffected.
2. An invalid subdomain now fails instead of being silently ignored. Callers passing a malformed value keep working against the shared host today; after this change they fail fast. This one is easy to miss because it is not what the ticket asked for, so it needs its own line in the release notes.

README

Updated in this PR: a "Subdomain value" section above the Default example, the subdomain added to the configuration samples, and a "Legacy domain (emergency use only)" section at the bottom.

Notes

The suite routes every client it builds through a single helper that uses the shared hosts. Applying the merchant-specific subdomain there looked better, since it is the path merchants are being moved to, but the sandbox OAuth clients are not provisioned for it: .NET CI failed 224 integration tests with invalid_client when the token request went to {subdomain}.access.sandbox.checkout.com. Binding those OAuth clients to the subdomain is a platform task and should land before merchants are told the subdomain is mandatory.

Reference implementation: checkout-sdk-net#590. Tracked as INT-1688.

No version bump here: that happens on master when the release is cut, per the release workflow.

---

Review follow-ups (2026-08-31)

Breaking changes, complete list:

1. The merchant-specific subdomain is now required; building without it (and without the legacy opt-out) throws.
2. An invalid subdomain now throws instead of being silently ignored.

Behaviour note: host resolution is now deferred to build time, which also fixes a latent order-dependence bug where setting the subdomain before the environment produced the wrong host.

Deprecation signal: documentation (docblock @deprecated).

Option A applied (2026-08-31): an explicit OAuth authorization URI and the environment subdomain are now mutually exclusive at build time; the README OAuth example no longer sets an authorization URI, subdomain-only is the documented path.

[agent-wall-e]

🔴 Risk Classification: MAJOR

Approval route: AI Review + Human Approval Required
Rollback controls: Change-freeze window + documented rollback plan

Classification reasons

• security_sensitive_path:test/Checkout/Tests/OAuthIntegrationTest.php

Operational gates

• ✅ jira_ticket (INT-1688)
• ✅ independent_review

Files analysed: 18

---

_{wall-e 2026.06.19-02 · policy 376219bc71e6…}

[agent-wall-e]

🔬 Debug — why this classification?

Each reason code emitted by the classifier, its source clause in the AI in SDLC Control Framework, and what it means.

Reason code	Kind	Clause	Meaning
security_sensitive_path — test/Checkout/Tests/OAuthIntegrationTest.php	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).

Kinds:

• classifying — this rule contributed to the chosen tier.
• informational — context only; did not by itself decide the tier.

See issue #3 for the proposal to formalise this map as Appendix A of the standards doc.

_{wall-e 2026.06.19-02 · debug}

[agent-wall-e]

🟠 Advisory review: Concerns worth a look

This PR needs a human approval. Before you give it, these are the things I'd want resolved.

The PR correctly enforces mandatory subdomain/legacy-domain configuration and fixes the order-dependence bug, but there are two concrete problems: a state-mutation hazard in getEnvironmentSubdomain() that can produce a cached EnvironmentSubdomain built against the wrong environment, and MetadataIntegrationTest calling .build() without .environment(...), which will now throw before the test can run.

Concerns

• In AbstractCheckoutSdkBuilder::getEnvironmentSubdomain(), a non-null $this->environmentSubdomain is returned as-is, but environment() resets $this->environmentSubdomain to null while leaving $this->subdomain intact — so the cache is only invalidated when environment() is called. However, if getEnvironmentSubdomain() is called twice (once from getSdkCredentials() in CheckoutOAuthSdkBuilder and once from build()), the second call returns the cached object, which is fine; but the broader point is that the private $environmentSubdomain field is now serving dual purpose (cache for the new lazy-build path AND the legacy direct-assignment path from environmentSubdomain()), and environmentSubdomain() nulls it out, so a call sequence of environmentSubdomain('x') -> getEnvironmentSubdomain() -> environment(prod) -> getEnvironmentSubdomain() would correctly rebuild, but environmentSubdomain('x') -> environment(prod) -> environmentSubdomain('x') -> getEnvironmentSubdomain() would re-build against prod, which is correct — this is actually fine; re-checking: the real hazard is that getEnvironmentSubdomain() in CheckoutOAuthSdkBuilder.getSdkCredentials() sets $this->authorizationUri from the freshly-built subdomain, then build() calls getEnvironmentSubdomain() again and may return a different (re-cached) instance if environment changed between calls — in practice the builder is single-use so this is low risk, but the dual-call in the OAuth builder (once in getSdkCredentials, once in build) is fragile and worth documenting or collapsing.
• In test/Checkout/Tests/Metadata/MetadataIntegrationTest.php, the createValidTokenRequest helper calls ->staticKeys()->publicKey(...)->secretKey(...)->environmentSubdomain(getenv("CHECKOUT_MERCHANT_SUBDOMAIN"))->build() with no ->environment(...) call — $this->environment will be null, causing EnvironmentSubdomain::__construct to call methods on null and likely throw a fatal error or a misleading exception rather than a useful one.
• The validateEnvironmentSettings() check on the OAuth builder runs after the authorizationUri+subdomain conflict check in build(), but getSdkCredentials() (called inside build() after those checks) also calls getEnvironmentSubdomain() which can throw a CheckoutArgumentException for an invalid subdomain — meaning the conflict check and the validation check happen in a different order than the exception message implies; this is a minor sequencing inconsistency but not a bug.
• The useLegacyDomain flag is a bool field with the same name as the useLegacyDomain() method in PHP, which is legal but can confuse static analysers; in Previous/CheckoutStaticKeysPreviousSdkBuilder, validateEnvironmentSettings() is now called, meaning a Previous builder that sets both subdomain and legacy domain will throw — this is intentional per the PR but is a subtle new constraint on a platform that was previously exempt, and the test suite does not appear to cover the Previous+both-set or Previous+subdomain-set cases.

---

_{This is not an approval. wall-e cannot auto-approve this PR — it is an opinion to help whoever does. Advisory review · us.anthropic.claude-sonnet-4-6 · wall-e 2026.06.19-02}

[agent-wall-e]

🔴 Risk Classification: MAJOR

Approval route: AI Review + Human Approval Required
Rollback controls: Change-freeze window + documented rollback plan

Classification reasons

• security_sensitive_path:.github/workflows/build-master.yml
• security_sensitive_path:.github/workflows/build-pull-request.yml
• security_sensitive_path:.github/workflows/build-release.yml
• security_sensitive_path:test/Checkout/Tests/OAuthIntegrationTest.php

Operational gates

• ✅ jira_ticket (INT-1688)
• ✅ independent_review

Files analysed: 21

---

_{wall-e 2026.06.19-02 · policy 376219bc71e6…}

[agent-wall-e]

🔬 Debug — why this classification?

Each reason code emitted by the classifier, its source clause in the AI in SDLC Control Framework, and what it means.

Reason code	Kind	Clause	Meaning
security_sensitive_path — .github/workflows/build-master.yml	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).
security_sensitive_path — .github/workflows/build-pull-request.yml	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).
security_sensitive_path — .github/workflows/build-release.yml	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).
security_sensitive_path — test/Checkout/Tests/OAuthIntegrationTest.php	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).

Kinds:

• classifying — this rule contributed to the chosen tier.
• informational — context only; did not by itself decide the tier.

See issue #3 for the proposal to formalise this map as Appendix A of the standards doc.

_{wall-e 2026.06.19-02 · debug}

[agent-wall-e]

🔴 Risk Classification: MAJOR

Approval route: AI Review + Human Approval Required
Rollback controls: Change-freeze window + documented rollback plan

Classification reasons

• security_sensitive_path:.github/workflows/build-master.yml
• security_sensitive_path:.github/workflows/build-pull-request.yml
• security_sensitive_path:.github/workflows/build-release.yml
• security_sensitive_path:test/Checkout/Tests/OAuthIntegrationTest.php

Operational gates

• ✅ jira_ticket (INT-1688)
• ✅ independent_review

Files analysed: 19

---

_{wall-e 2026.06.19-02 · policy 376219bc71e6…}

[agent-wall-e]

🔬 Debug — why this classification?

Each reason code emitted by the classifier, its source clause in the AI in SDLC Control Framework, and what it means.

Reason code	Kind	Clause	Meaning
security_sensitive_path — .github/workflows/build-master.yml	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).
security_sensitive_path — .github/workflows/build-pull-request.yml	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).
security_sensitive_path — .github/workflows/build-release.yml	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).
security_sensitive_path — test/Checkout/Tests/OAuthIntegrationTest.php	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).

Kinds:

• classifying — this rule contributed to the chosen tier.
• informational — context only; did not by itself decide the tier.

See issue #3 for the proposal to formalise this map as Appendix A of the standards doc.

_{wall-e 2026.06.19-02 · debug}

[agent-wall-e]

🔴 Risk Classification: MAJOR

Approval route: AI Review + Human Approval Required
Rollback controls: Change-freeze window + documented rollback plan

Classification reasons

• security_sensitive_path:test/Checkout/Tests/OAuthIntegrationTest.php

Operational gates

• ✅ jira_ticket (INT-1688)
• ✅ independent_review

Files analysed: 15

---

_{wall-e 2026.06.19-02 · policy 376219bc71e6…}

[agent-wall-e]

🔬 Debug — why this classification?

Each reason code emitted by the classifier, its source clause in the AI in SDLC Control Framework, and what it means.

Reason code	Kind	Clause	Meaning
security_sensitive_path — test/Checkout/Tests/OAuthIntegrationTest.php	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).

Kinds:

• classifying — this rule contributed to the chosen tier.
• informational — context only; did not by itself decide the tier.

See issue #3 for the proposal to formalise this map as Appendix A of the standards doc.

_{wall-e 2026.06.19-02 · debug}

[agent-wall-e]

🔴 Risk Classification: MAJOR

Approval route: AI Review + Human Approval Required
Rollback controls: Change-freeze window + documented rollback plan

Classification reasons

• security_sensitive_path:test/Checkout/Tests/OAuthIntegrationTest.php

Operational gates

• ✅ jira_ticket (INT-1688)
• ✅ independent_review

Files analysed: 17

---

_{wall-e 2026.06.19-02 · policy 376219bc71e6…}

[agent-wall-e]

🔬 Debug — why this classification?

Each reason code emitted by the classifier, its source clause in the AI in SDLC Control Framework, and what it means.

Reason code	Kind	Clause	Meaning
security_sensitive_path — test/Checkout/Tests/OAuthIntegrationTest.php	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).

Kinds:

• classifying — this rule contributed to the chosen tier.
• informational — context only; did not by itself decide the tier.

See issue #3 for the proposal to formalise this map as Appendix A of the standards doc.

_{wall-e 2026.06.19-02 · debug}

[agent-wall-e]

🔴 Risk Classification: MAJOR

Approval route: AI Review + Human Approval Required
Rollback controls: Change-freeze window + documented rollback plan

Classification reasons

• security_sensitive_path:test/Checkout/Tests/OAuthIntegrationTest.php

Operational gates

• ✅ jira_ticket (INT-1688)
• ✅ independent_review

Files analysed: 15

---

_{wall-e 2026.06.19-02 · policy 376219bc71e6…}

[agent-wall-e]

🔬 Debug — why this classification?

Each reason code emitted by the classifier, its source clause in the AI in SDLC Control Framework, and what it means.

Reason code	Kind	Clause	Meaning
security_sensitive_path — test/Checkout/Tests/OAuthIntegrationTest.php	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).

Kinds:

• classifying — this rule contributed to the chosen tier.
• informational — context only; did not by itself decide the tier.

See issue #3 for the proposal to formalise this map as Appendix A of the standards doc.

_{wall-e 2026.06.19-02 · debug}

[agent-wall-e]

🔴 Risk Classification: MAJOR

Approval route: AI Review + Human Approval Required
Rollback controls: Change-freeze window + documented rollback plan

Classification reasons

• security_sensitive_path:test/Checkout/Tests/OAuthIntegrationTest.php

Operational gates

• ✅ jira_ticket (INT-1688)
• ✅ independent_review

Files analysed: 16

---

_{wall-e 2026.06.19-02 · policy 376219bc71e6…}

[agent-wall-e]

🔬 Debug — why this classification?

Each reason code emitted by the classifier, its source clause in the AI in SDLC Control Framework, and what it means.

Reason code	Kind	Clause	Meaning
security_sensitive_path — test/Checkout/Tests/OAuthIntegrationTest.php	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).

Kinds:

• classifying — this rule contributed to the chosen tier.
• informational — context only; did not by itself decide the tier.

See issue #3 for the proposal to formalise this map as Appendix A of the standards doc.

_{wall-e 2026.06.19-02 · debug}

[agent-wall-e]

🔴 Risk Classification: MAJOR

Approval route: AI Review + Human Approval Required
Rollback controls: Change-freeze window + documented rollback plan

Classification reasons

• security_sensitive_path:test/Checkout/Tests/OAuthIntegrationTest.php

Operational gates

• ✅ jira_ticket (INT-1688)
• ✅ independent_review

Files analysed: 15

---

_{wall-e 2026.06.19-02 · policy 376219bc71e6…}

[agent-wall-e]

🔬 Debug — why this classification?

Each reason code emitted by the classifier, its source clause in the AI in SDLC Control Framework, and what it means.

Reason code	Kind	Clause	Meaning
security_sensitive_path — test/Checkout/Tests/OAuthIntegrationTest.php	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).

Kinds:

• classifying — this rule contributed to the chosen tier.
• informational — context only; did not by itself decide the tier.

See issue #3 for the proposal to formalise this map as Appendix A of the standards doc.

_{wall-e 2026.06.19-02 · debug}

[agent-wall-e]

🔴 Risk Classification: MAJOR

Approval route: AI Review + Human Approval Required
Rollback controls: Change-freeze window + documented rollback plan

Classification reasons

• security_sensitive_path:test/Checkout/Tests/OAuthIntegrationTest.php

Operational gates

• ✅ jira_ticket (INT-1688)
• ✅ independent_review

Files analysed: 16

---

_{wall-e 2026.06.19-02 · policy 376219bc71e6…}

[agent-wall-e]

🔬 Debug — why this classification?

Each reason code emitted by the classifier, its source clause in the AI in SDLC Control Framework, and what it means.

Reason code	Kind	Clause	Meaning
security_sensitive_path — test/Checkout/Tests/OAuthIntegrationTest.php	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).

Kinds:

• classifying — this rule contributed to the chosen tier.
• informational — context only; did not by itself decide the tier.

See issue #3 for the proposal to formalise this map as Appendix A of the standards doc.

_{wall-e 2026.06.19-02 · debug}

[agent-wall-e]

🔴 Risk Classification: MAJOR

Approval route: AI Review + Human Approval Required
Rollback controls: Change-freeze window + documented rollback plan

Classification reasons

• security_sensitive_path:test/Checkout/Tests/OAuthIntegrationTest.php

Operational gates

• ✅ jira_ticket (INT-1688)
• ✅ independent_review

Files analysed: 17

---

_{wall-e 2026.06.19-02 · policy 376219bc71e6…}

[agent-wall-e]

🔬 Debug — why this classification?

Each reason code emitted by the classifier, its source clause in the AI in SDLC Control Framework, and what it means.

Reason code	Kind	Clause	Meaning
security_sensitive_path — test/Checkout/Tests/OAuthIntegrationTest.php	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).

Kinds:

• classifying — this rule contributed to the chosen tier.
• informational — context only; did not by itself decide the tier.

See issue #3 for the proposal to formalise this map as Appendix A of the standards doc.

_{wall-e 2026.06.19-02 · debug}

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud