Add a webhook handler for Stellar Horizon transaction events to update key ownership records

[Chucks1093]

Summary

Key ownership updates currently depend on polling. A webhook handler that receives Stellar Horizon payment and account events should update ownership records in real time, reducing latency between on-chain settlement and off-chain state.

Scope

• Expose a POST /webhooks/horizon endpoint to receive Horizon event callbacks
• Verify the HMAC-SHA256 signature on every incoming webhook payload
• Parse payment_received and transaction_successful event types
• Match the transaction memo to a pending key purchase order
• Update the owner field on the key record and emit an internal ownership_transferred event

Acceptance Criteria

• Endpoint rejects requests with invalid HMAC signatures with 401
• payment_received events update key ownership correctly
• Unmatched memos are logged and discarded without error
• Duplicate event delivery is idempotent
• ownership_transferred event emitted after successful update

ETA: 12 hours

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Coordinate on Telegram

[Jumongweb]

@Jumongweb has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi maintainer, i will like to solve this issue

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[Hamzasaheed]

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Hi Maintainer,
I’m interested in taking on this issue.
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I’m confident I can deliver a quality solution.
I’m available to start immediately.

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[salamatabdulkarim-stack]

@salamatabdulkarim-stack has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hello maintainer I would like to work on this issue, Thank you

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[teethaking]

hello maintainer may i work on this issue?
ill submit PR within 1-3 days

[smog123]

@smog123 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

please assuign

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[teethaking]

hello maintainer may i work on this issue?
ill submit PR within 1-3 days

[Akanimoh12]

@Akanimoh12 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi, I'd love to work on this issue. I'm a full-stack blockchain developer specializing in web apps and Smart Contracts, with experience in Next.js, TypeScript, Tailwind, and blockchain integration's and writing tests. I can handle this confidently, here's my portfolio and key projects:

• https://frontend-nine-mocha.vercel.app/
• https://i-predict.vercel.app/
• https://somnia-screams.vercel.app/
• https://chessflip-celo.vercel.app/

Active OSS contributor.

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Congratulations, @Akanimoh12! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on August 31, 2026.

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[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Third Campaign campaign!

@Akanimoh12's PR #790 was approved and merged by @Chucks1093.

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👏 Great work, @Akanimoh12! Keep contributing to accesslayerorg.

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