fix(auth): harden JWT cookie with secure and sameSite flags

[sricharan12-hub]

Overview

Hardens the authentication JWT cookie in backend/src/controllers/userAuth.js.
Previously the cookie was set with only httpOnly, so it was attached to
cross-site requests (no CSRF protection) and could be sent over plain HTTP in
production.

Closes #83

Changes

• Define a shared cookieOptions object with secure and sameSite:
  • secure: isProd — HTTPS-only in production, off in local HTTP development.
  • sameSite: isProd ? "none" : "lax" — "none" supports a cross-site
    frontend/API in production (requires secure), "lax" keeps local dev working.
• Reuse cookieOptions in register, login, and logout so the cookie is
  set and cleared with matching attributes — required for the browser to
  reliably remove it on logout.

httpOnly (JS-access protection) is preserved; this adds CSRF and
insecure-transport protection on top.

Acceptance criteria

• Auth cookie is set with sameSite and secure (secure enabled in production).
• The same attributes are applied in register, login, and logout.
• Login/logout continue to work in local development (HTTP) and in production (HTTPS).

Testing

• node --check passes and the module imports cleanly (import() resolves without error).
• In development (NODE_ENV !== "production"): secure=false, sameSite=lax — cookie works over local HTTP.
• In production (NODE_ENV === "production"): secure=true, sameSite=none — cookie restricted to HTTPS.

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📥 Commits

Reviewing files that changed from the base of the PR and between 87148ba and da74ae8.

📒 Files selected for processing (1)

• backend/src/controllers/userAuth.js

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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