fix(security): verify Meta webhook HMAC signature (Batch B) - #6
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…y-token Batch B (Meta-direct). The webhook POST accepted any forged JSON. Now: - Capture the raw request body (express.json verify hook) and verify X-Hub-Signature-256 (HMAC-SHA256 with META_APP_SECRET) using timingSafeEqual; reject with 403 on mismatch. When META_APP_SECRET is unset, log a warning (unverified) rather than breaking existing deployments. - Make the GET verify-token comparisons constant-time (safeEqual) to remove the timing oracle. Audit ref: REVIEW.md P0 #2 (lane 06 CRITICAL + HIGHs). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com> Signed-off-by: KingArthur000 <sathyaprakashelango@gmail.com>
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Batch B — webhook authenticity (REVIEW.md P0 #2, lane 06 CRITICAL). The POST webhook accepted any forged JSON. Now verifies Meta's
X-Hub-Signature-256(HMAC-SHA256 over the raw body withMETA_APP_SECRET,timingSafeEqual) and rejects mismatches with 403; warns when unconfigured. Verify-token compares are now constant-time. Meta-direct topology per your choice.