Refactor: Implement Webhook Signature Verification

[Smartdevs17]

Description\nImplement webhook signature verification for all incoming webhooks to prevent spoofed callbacks from payment providers, webhooks, and other services.\n\nCurrent Limitation: No webhook verification.\nExpected Outcome: HMAC verification for all webhooks with retry logic for invalid signatures.\n## Acceptance Criteria\n- [ ] HMAC-SHA256 verification\n- [ ] Per-provider secrets\n- [ ] Timestamp verification (replay protection)\n- [ ] Signature validation on all incoming\n- [ ] Failed webhook queuing\n- [ ] Manual retry\n- [ ] Secret rotation\n- [ ] Verification logs\n## Technical Scope\n- Files: backend/webhooks/verification\n- Edge Cases: Clock skew, algorithm mismatch\n## Complexity Estimate\n200 points - Verification, secure storage.

[chiemezie1]

@chiemezie1 has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

Hi, I will like to work on this task.
This is what I will do: implement HMAC-SHA256 webhook signature verification for all incoming requests, add per-provider secret management, enforce timestamp-based replay protection, handle invalid signatures with failed webhook queuing and retry support, include secret rotation, and ensure proper verification logging across all webhook flows.
Can I be assigned?

ℹ️ Repo Maintainers: To accept this application, review their application or assign @chiemezie1 to this issue.

[drips-wave]

Congratulations, @chiemezie1! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on April 29, 2026.

🧑‍💻 @chiemezie1: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

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