feat(pkce): Default clientId to the client's configured client ID

[gjtorikian]

Summary

• Makes $clientId optional across all four PKCEHelper flows — getAuthKitAuthorizationUrl, authKitCodeExchange, getSsoAuthorizationUrl, and ssoCodeExchange — falling back to $this->client->requireClientId() when omitted.
• Callers no longer have to re-pass a client ID the WorkOS client already carries (constructor argument or WORKOS_CLIENT_ID env var), aligning the PHP SDK with the override-with-fallback pattern used by the other backend SDKs.
• Explicitly passed client IDs still take precedence over the configured one.
• An unconfigured client now throws a ConfigurationException with a clear message instead of a TypeError from the missing required parameter.
• Adds tests covering the fallback, the explicit-argument override, and the ConfigurationException path for both authorization-URL and code-exchange flows.

[greptile-apps]

Greptile Summary

Makes the client ID optional in all four PKCE authorization and code-exchange flows.

• Falls back to the WorkOS client's configured client ID when no explicit value is supplied.
• Preserves explicit client-ID overrides and raises ConfigurationException when neither source is configured.
• Adds tests for configured fallback, explicit override, and missing configuration behavior.

Confidence Score: 5/5

The PR appears safe to merge.

All four changed methods preserve explicit client IDs, resolve omitted values through the existing configuration guard, and pass the resolved value into the correct request field.

Important Files Changed

Filename	Overview
lib/PKCEHelper.php	Consistently resolves omitted client IDs through requireClientId() before constructing each AuthKit and SSO request.
tests/PKCEHelperTest.php	Adds focused coverage for fallback, override, and missing-client-ID behavior without revealing a functional regression.

_{Reviews (1): Last reviewed commit: "feat(pkce): default clientId to the clie..." | Re-trigger Greptile}