Add explicit require_auth protections for subscriber cancellation and tier downgrades

[elizabetheonoja-art]

Task: Add explicit require_auth protections for subscriber cancellation and tier downgrades

Focus Area: Soroban Smart Contract Optimization, Security Hardening, and Reliability.

[khanavi272-spec]

@khanavi272-spec has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

I would like to work on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @khanavi272-spec to this issue.

[jiyiola396-pixel]

@jiyiola396-pixel has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

hi maintainer,
i would like to work on this issue.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @jiyiola396-pixel to this issue.

[drips-wave]

Congratulations, @jiyiola396-pixel! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on April 29, 2026.

🧑‍💻 @jiyiola396-pixel: 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.

Warning

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊