Add zod input validation for /api/auth

[greatest0fallt1me]

Description

This is a backend issue for the GrantFox FWC26 campaign (Stellar Wave). Zod-validated request schema for /api/auth with structured 400 errors.

Requirements and Context

• Implement per the description above
• Add focused tests for the change
• Document any API/visible changes
• Adhere to repo's lint and code style
• Must be secure, tested, and documented

Suggested Execution

1. Fork the repo and create a branch
2. Implement changes:
   • src/routes/auth.ts
   • src/validators/auth.ts
3. Test and commit; open a PR with Closes #486 in the body

Guidelines

• Minimum 90% test coverage on changed lines
• Input validation at the boundary; standardized error envelope
• Structured logging with correlation IDs
• Clear documentation and inline comments
• Timeframe: 96 hours

[Ayinkx]

@Ayinkx has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hi i would like to work on this issue
please

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

[drips-wave]

Congratulations, @Ayinkx! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on July 30, 2026.

🧑‍💻 @Ayinkx: 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 🌊

[greatest0fallt1me]

Hey @Ayinkx 👋 — you've been assigned to this issue based on your DripsWave application.

Quick reminders:

• Draft PR early and link it with Closes #<issue-number> so the DripsWave bot auto-closes.
• Please respect the 4 assignments per org cap (DripsWave auto-unassigns beyond that).
• Ping in Discord for questions or unblocks: https://discord.gg/WC53JxDqx

Looking forward to your PR — good luck! 🚀