[PM-24211]: 2FA Send Email Login validation should use AuthRequest.IsValidForAuthentication

[enmande]

🎟️ Tracking

PM-24211

📔 Objective

Update the 2FA Send Email Login action to use AuthRequest.IsValidForAuthentication evaluation. This helper is more consistently preferred for validation scenarios, to ensure parity across validation schemes and facilitate maintenance.

The replaced command, having a single call site, has been removed.

📸 Screenshots

See PM-24211

Log in with Device, Email 2FA Required

PM-24211__email-login-with-device.mov

⏰ Reminders before review

• Contributor guidelines followed
• All formatters and local linters executed and passed
• Written new unit and / or integration tests where applicable
• Protected functional changes with optionality (feature flags)
• Used internationalization (i18n) for all UI strings
• CI builds passed
• Communicated to DevOps any deployment requirements
• Updated any necessary documentation (Confluence, contributing docs) or informed the documentation team

🦮 Reviewer guidelines

• 👍 (:+1:) or similar for great changes
• 📝 (:memo:) or ℹ️ (:information_source:) for notes or general info
• ❓ (:question:) for questions
• 🤔 (:thinking:) or 💭 (:thought_balloon:) for more open inquiry that's not quite a confirmed issue and could potentially benefit from discussion
• 🎨 (:art:) for suggestions / improvements
• ❌ (:x:) or ⚠️ (:warning:) for more significant problems or concerns needing attention
• 🌱 (:seedling:) or ♻️ (:recycle:) for future improvements or indications of technical debt
• ⛏ (:pick:) for minor or nitpick changes

[github-actions]

Checkmarx One – Scan Summary & Details – 01cb1ca0-4f68-4d87-8aa4-7821a81a9299

Great job! No new security vulnerabilities introduced in this pull request

[codecov]

Codecov Report

❌ Patch coverage is 33.33333% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.46%. Comparing base (b0f6b22) to head (77234c1).
⚠️ Report is 18 commits behind head on main.

Files with missing lines	Patch %	Lines
src/Api/Auth/Controllers/TwoFactorController.cs	33.33%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6695      +/-   ##
==========================================
+ Coverage   53.41%   57.46%   +4.05%     
==========================================
  Files        1917     1924       +7     
  Lines       85467    85705     +238     
  Branches     7667     7686      +19     
==========================================
+ Hits        45651    49254    +3603     
+ Misses      38048    34606    -3442     
- Partials     1768     1845      +77     

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[claude]

Claude finished @enmande's task —— View job

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Code Review Complete

Tasks

• Analyze PR changes with Bitwarden code reviewer
• Review security implications
• Assess test coverage
• Provide comprehensive feedback

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Review Findings

I've completed a thorough review of this PR that refactors 2FA email login validation from using a dedicated VerifyAuthRequestCommand to using AuthRequest.IsValidForAuthentication.

✅ Security Enhancement (Positive)

The refactoring significantly improves security. The old VerifyAuthRequestCommand only verified:

• Auth request exists
• Access code matches

The new IsValidForAuthentication method validates 7 additional security conditions:

• Response date exists (request has been responded to)
• Approved == true (request was approved, not denied)
• Not expired (respects 15-minute timeout)
• Correct type (AuthenticateAndUnlock only)
• Not already used (prevents replay attacks)
• User ID matches
• Access code matches (using timing-safe comparison)

This prevents several attack vectors including replay attacks and authorization bypasses.

📝 Critical Bug Fix Identified

The addition of the return statement on line 360 in src/Api/Auth/Controllers/TwoFactorController.cs:360 is a critical bug fix. Without this return, the validation would fall through to other validation branches, potentially causing unintended behavior. This fix should be highlighted in the PR description.

⚠️ Test Coverage Gap

The Codecov report correctly identifies missing test coverage. Here's what I found:

Well-tested: AuthRequest.IsValidForAuthentication has 9 comprehensive unit tests covering all validation paths (excellent work on test/Core.Test/Auth/Entities/AuthRequestTests.cs)

Not tested: TwoFactorController.SendEmailLoginAsync has zero tests for the auth request validation path (lines 352-362)

Specific missing coverage in src/Api/Auth/Controllers/TwoFactorController.cs:

• Line 355: var authRequest = await _authRequestRepository.GetByIdAsync(...)
• Lines 356-357: The null check and IsValidForAuthentication condition
• Line 359: await _twoFactorEmailService.SendTwoFactorEmailAsync(user)
• Line 360: The new return statement

🌱 Recommendations

1. Add tests for TwoFactorController.SendEmailLoginAsync covering:

   • Valid auth request → should send email and return
   • Invalid auth request (null) → should not send email, continue to SSO validation
   • Invalid auth request (validation fails) → should not send email, continue to SSO validation
   • Valid auth request with wrong user → should not send email

2. Document the return statement bug fix in the PR description - The addition of return on line 360 is a critical fix that prevents fall-through to other validation branches

3. Consider integration test - While unit tests are good, an integration test verifying the full 2FA email flow would provide additional confidence

🎨 Code Quality

Positive observations:

• Entity-based validation aligns with domain-driven design
• Uses timing-safe comparison (CoreHelpers.FixedTimeEquals) to prevent timing attacks
• Comprehensive test coverage for the entity method
• Removes unnecessary abstraction layer (command pattern was overkill for this use case)
• Comment improvements clarify intent

Minor note:

• Both files still use #nullable disable (technical debt, not blocking)

ℹ️ Breaking Change Assessment

The validation is now stricter. However, based on my analysis:

• Only 2 locations use this validation: TwoFactorController.SendEmailLoginAsync and ResourceOwnerPasswordValidator
• Both appear to expect the stricter validation semantics
• This is intentional security hardening, not an accidental breaking change

Summary

This is a well-executed refactoring that improves security, removes unnecessary abstraction, and includes good entity-level tests. The main gap is missing controller-level tests for the modified code path. The 33.33% coverage issue is entirely due to the untested controller method, not the entity logic.

Recommendation: Add tests for TwoFactorController.SendEmailLoginAsync, then this is ready to merge. The security improvements and bug fix (return statement) are valuable contributions that enhance the authentication flow.

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[JaredSnider-Bitwarden]

Excellent work! Thank you for your patience in the requested tweaks!