fix(auth): exclude password hash from req.user in deserializeUser

[anshul23102]

Summary

Fixes #555

deserializeUser called User.findById(id) with no field projection, attaching the full Mongoose document (including the password bcrypt hash) to req.user on every authenticated request.

Risk

Any route handler that returns req.user to the client — a profile endpoint, an admin panel, or a future /api/auth/me — would include the password field in the response without the author realising it. A leaked bcrypt hash is directly attackable offline with GPU-accelerated wordlist cracking.

Change

backend/config/passportConfig.js

// Before
const user = await User.findById(id);

// After
const user = await User.findById(id).select('-password -__v').lean();

• .select('-password -__v') excludes the hash and the internal __v version key.
• .lean() returns a plain JS object instead of a Mongoose document, so model methods are not accessible via req.user.

Test Plan

• Login and call any authenticated endpoint that returns req.user. Confirm the response does not contain a password field.
• Confirm req.user.comparePassword is undefined (lean object has no model methods).

Important

GSSoC'26 contribution - Please add labels (gssoc26, type:security, level:intermediate) to help with point tracking. Thank you!

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Reviewing files that changed from the base of the PR and between 4ae0ef6 and 55706df.

📒 Files selected for processing (1)

• backend/config/passportConfig.js

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[anshul23102]

Hey @GitMetricsLab, pinging this as part of NSoC'26. Happy to make any adjustments you need. Thanks!