🧹 [code health] Refactor monolithic Auth controller method logic by extracting cookie helpers

[Adityavanjre]

🎯 What: Extracted response cookie settings into an auth helper module.
💡 Why: Centralizes the core authentication cookie management logic, making the AuthController less monolithic and the cookie setup logic reusable and easier to test independently. This improves code health and maintainability.
✅ Verification: Verified by ensuring the code logic is 1:1 with previous execution, running the test suite to ensure no tests regressed, and validating with code review tooling.
✨ Result: A highly modular, cleaner auth.controller.ts with no behavioral changes.

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PR created automatically by Jules for task 9033528662927682081 started by @Adityavanjre

Summary by CodeRabbit

• Refactor
  • Reorganized authentication cookie management to centralize handling and ensure consistent security practices across login, logout, and token refresh flows.

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 6051811 and e082bfc.

📒 Files selected for processing (2)

• nexus/backend/src/auth/auth.controller.ts
• nexus/backend/src/auth/helpers/cookie.helper.ts

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📝 Walkthrough

Walkthrough

This PR refactors authentication cookie management by extracting cookie-setting and cookie-clearing logic from the auth controller into a reusable helper module. The helper centralizes CSRF token generation and cookie attribute configuration, while the controller now delegates all cookie operations to these shared functions across login, registration, MFA, refresh, and logout flows.

Changes

Auth Cookie Helper Extraction

Layer / File(s)	Summary
Cookie Helper Functions nexus/backend/src/auth/helpers/cookie.helper.ts	New setAuthCookies function sets nexus_token (HTTP-only, 1d), optional nexus_refresh (HTTP-only, 7d), and CSRF nexus-csrf (non-HTTP-only, 1d). New clearAuthCookies clears token and refresh cookies.
Controller Integration nexus/backend/src/auth/auth.controller.ts	Auth controller imports helpers and replaces all internal cookie-setting calls across login, register, MFA, refresh endpoints with setAuthCookies(...) and logout with clearAuthCookies(res). Internal setAuthCookies implementation removed.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

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