Add WebhookSignatureValidator utility#340
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Verifies MercadoPago webhook notifications by recomputing the HMAC-SHA256 signature locally and comparing it in constant time (MessageDigest.isEqual) against the value in the x-signature header. Stateless, performs no outbound HTTP calls. - com.mercadopago.webhook.WebhookSignatureValidator - com.mercadopago.exceptions.MPInvalidWebhookSignatureException (extends MPException; checked; Lombok @Getter) - com.mercadopago.exceptions.SignatureFailureReason enum - Optional Duration tolerance for replay protection - Forward-compatible supportedVersions parameter (default List.of("v1")) - 16 JUnit 5 tests covering the canonical cases Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>
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Summary
Adds a stateless utility to verify the authenticity of incoming MercadoPago webhook notifications by recomputing the HMAC-SHA256 signature and comparing it against the
x-signatureheader in constant time (timing-attack safe).Changes
webhook/WebhookSignatureValidator.java: HMAC-SHA256 validator with explicit secret per call, no MercadoPagoConfig dependencyexceptions/MPInvalidWebhookSignatureException.java: typed exception thrown on validation failuresexceptions/SignatureFailureReason.java: enum of specific failure reasons (missing header, malformed signature, hash mismatch, etc.)webhook/WebhookSignatureValidatorTest.java: unit tests covering success, malformed inputs, timestamp window, hash mismatchTest plan