fix: store password reset code as keyed HMAC instead of cleartext (#507)

[RounakKumarAgarwal]

Description

Fixes #507

The password reset code was stored in the database as cleartext, so anyone with DB read access could brute-force all ~10^6 six-digit codes offline and reset any account's password (flagged as CWE-312 / CWE-922 during review of #506).

This stores a keyed HMAC-SHA256 of the code instead of the plaintext:

• ForgotPassword stores HMAC(code, secret) but still emails the plaintext code to the user.
• VerifyForgotPassword hashes the submitted code the same way and matches on the hash — in both the lookup and the atomic update filter introduced in fix: expire password reset codes after 15 minutes (#485) #506.

Keyed with the existing JWT secret (cfg.JWT.Secret), so no new config is required. HMAC is deterministic, so it stays compatible with the exact-match lookup/update filter. The plaintext code is never persisted.

Migration note: reset codes issued before this deploys (stored as plaintext) won't match the new HMAC lookup and will fall through to reissue — the user requests a new code. Given the 15-minute expiry (#506), this window is small and self-healing; deliberately not adding a plaintext-compatibility path so the reset flow never matches plaintext again.

Changes

• New backend/controllers/reset_code.go — hashResetCode helper (HMAC-SHA256, hex-encoded).
• backend/controllers/auth.go — store the HMAC in ForgotPassword; hash and compare in VerifyForgotPassword.

Testing

Verified locally end-to-end:

• After requesting a reset, resetPasswordCode in the DB is stored as a 64-char HMAC, not the 6-digit code:

• resetPasswordCode: 'af7e301381c18a5f2e20ffbc1cff6c881aec5a28d12f59353920790a372637d2'

• Resetting the password with the emailed plaintext code still succeeds, confirming the store/verify hashing round-trips correctly.

• go build ./controllers/ passes.

Notes

• No migration needed: reset codes expire after 15 minutes (fix: expire password reset codes after 15 minutes (#485) #506), so any pre-existing cleartext codes are already invalid.
• Keyed with the existing JWT secret to avoid adding new config; happy to switch to a dedicated secret if you'd prefer.

Summary by CodeRabbit

• Security
  • Password reset codes are now stored securely in hashed form rather than plaintext.
  • Password reset emails continue to provide recipients with the code needed to complete the reset process.

[coderabbitai]

📝 Walkthrough

Walkthrough

Password reset codes are now stored as HMAC-SHA256 digests using the JWT secret. Verification hashes the submitted code before database matching. The plaintext code remains in the reset email.

Changes

Password reset code protection

Layer / File(s)	Summary
HMAC reset-code storage and verification backend/controllers/reset_code.go, backend/controllers/auth.go	Added a private HMAC-SHA256 helper. ForgotPassword stores the hexadecimal digest, while VerifyForgotPassword uses the digest for lookup and update matching. The email still receives the plaintext code.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix · Severity of issue fixed: Medium

Merge Risk: 🔵 Low · up to 4e55e

Users with a reset code issued just before deployment may be unable to complete the reset until they request a new code, creating a bounded interruption in the password-reset flow.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Issue #507 requires keyed protection for the six-digit reset code and matching verification. ForgotPassword stores hashResetCode(resetCode, cfg.JWT.Secret). VerifyForgotPassword uses the same HM…
Out of Scope Changes check	✅ Passed	The code changes are limited to the password reset flow and its hash helper. They do not add unrelated behavior, configuration, or data changes. The changes remain within issue #507 scope.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: storing password reset codes as keyed HMAC values instead of cleartext.

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Actionable comments posted: 1

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Inline comments:
In `@backend/controllers/auth.go`:
- Around line 469-470: Update VerifyForgotPassword around hashResetCode and the
users collection lookup to support unexpired legacy plaintext resetPasswordCode
values during the transition window. Prefer an atomic, single-use migration or
consumption path whose update filter matches the plaintext representation, while
preserving the existing HMAC validation; alternatively invalidate legacy codes
and explicitly force reissue rather than returning an ambiguous failure.

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ℹ️ Review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 9f90f9b and 4e55ef7.

📒 Files selected for processing (2)

• backend/controllers/auth.go
• backend/controllers/reset_code.go

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