fix: add webhook timestamp validation for replay attack protection (issue #23)

[tmdeveloper007]

Summary

Adds timestamp validation to the GitHub webhook handler to prevent replay attacks. Webhook events older than 5 minutes (GitHub-recommended threshold) are now rejected with HTTP 400.

The validation extracts the event timestamp from the payload (pull_request.updated_at, issue.updated_at, or head_commit.timestamp) and compares it against the current time.

Issue

Fixes #23: Verify GitHub webhook signatures (+ replay protection)

Changes

• Added MAX_WEBHOOK_AGE_MS constant (5 minutes)
• Added extractEventTimestamp() helper to extract timestamp from payload
• Added validateWebhookTimestamp() function that returns validity + reason
• Added timestamp validation step in the POST handler after JSON parsing and before event routing
• Returns 400 with reason when a stale webhook is detected

Security Impact

Prevents replay attacks where an attacker with a valid signed webhook reuses it after the valid time window.

Files Changed

• app/api/integrations/github/webhook/route.ts

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📥 Commits

Reviewing files that changed from the base of the PR and between 07ceab7 and 162111c.

📒 Files selected for processing (1)

• app/api/integrations/github/webhook/route.ts

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[github-actions]

🎉 Thanks for your contribution, @tmdeveloper007!

Your PR has passed our automated GSSoC quality checks. Here's a quick summary:

Check	Status
PR description	✅ Provided
PR title	✅ Meaningful
Linked issue	✅ Found
Change size	✅ Looks good (54 lines across 1 file(s))

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GSSoC'26 automation · Maintainer: @nisshchayarathi

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