fix(login): prevent user enumeration via differential password reset UI

[DeepDiver1975]

Summary

• showLoginForm() showed different UI for LDAP users (no "Reset it?" link) vs non-existent users, creating an unauthenticated oracle to enumerate LDAP users
• Fix removes the canChangePassword() backend check; canResetPassword is always true unless lost_password_link=disabled
• Response is now identical for LDAP users, standard users, and non-existent users

Security Impact

Low — user enumeration limited to backends without password-change support (e.g. LDAP); requires login attempts

Note

This PR touches the same files as security/fix-login-brute-force — merge that one first.

Test plan

• testShowLoginFormCanResetPasswordUniformForNonExistentUser and updated existing tests assert canResetPassword=true regardless of backend type; fail without fix
• Run make test TEST_PHP_SUITE=core/Controller

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[update-docs]

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[DeepDiver1975]

Code Review — fix(login): prevent user enumeration via differential password reset UI

Overview: Removes the per-user canChangePassword() check that caused the "Reset it?" link to appear only for valid LDAP accounts, leaking user existence to unauthenticated callers. The reset link now shows unconditionally (unless lost_password_link is set to disabled).

Correctness

The fix is correct and complete. The key change is removing the if ($userObj instanceof IUser) { $parameters['canResetPassword'] = $userObj->canChangePassword(); } block, so canResetPassword defaults to true for all users regardless of existence or backend type. This collapses the differential response.

The loginName logic refactor is also correct: setting $parameters['loginName'] = $user unconditionally first and then overriding it only when $u->getUserName() returns a non-empty string is cleaner and logically equivalent to the previous two-step check.

Tests

Two new tests are well-targeted:

• testShowLoginFormWithPasswordResetOptionAlwaysTrueWhenNoLostPasswordLink — verifies canChangePassword is never called and canResetPassword is always true for a valid user
• testShowLoginFormCanResetPasswordUniformForNonExistentUser — explicitly tests the enumeration case (non-existent user must yield same canResetPassword=true as a valid user)

Both testShowLoginFormForUserNamedNull updates are correct (same fix applied).

One minor note

The $parameters['user_autofocus'] = false line remains inside the if ($u !== null && ...) branch. This means user_autofocus is only set to false when a valid user with a non-empty username is found; for non-existent users it falls through to the else branch where user_autofocus is not set. This was the pre-existing behaviour and is not changed by this PR — not an issue introduced here.

Summary

Aspect	Assessment
Security fix	✅ Correct — differential response eliminated
Tests	✅ Both enumeration cases explicitly covered
Regression risk	Low — only the reset-link visibility changes

Verdict: Ready to merge.

[DeepDiver1975]

Code Review — fix(login): prevent user enumeration via differential password reset UI (updated)

Overview: This is a significant rewrite of the PR compared to the previously-reviewed version. It now includes a full diff of LoginController.php with the user-enumeration fix and also cleans up a duplicate loginName assignment block.

User enumeration fix

Before: canResetPassword was set to false when a valid user existed on a backend where canChangePassword() returned false (e.g. LDAP). This made login-form responses distinguishable: LDAP user → no reset link, non-existent user → no reset link but for different reasons. In practice the original code set canResetPassword based on $userObj->canChangePassword(), which leaked the existence of a user on backends that don't support password change.

After: canResetPassword is unconditionally true unless lost_password_link === 'disabled'. The backend capability check is removed entirely. ✅

loginName resolution cleanup

The PR also removes a duplicated loginName/user_autofocus assignment block that appeared after the alt_login section and was clobbering the LDAP username resolution:

// Removed — this block was overwriting $parameters['loginName'] back to
// the raw $user value after the UUID→displayName resolution above.
if ($user !== null && $user !== '') {
    $parameters['loginName'] = $user;
    ...
}

The earlier block correctly resolves $u->getUserName() when the user object exists; the later redundant block was resetting it. Removal is correct. ✅

Test changes

testShowLoginFormWithPasswordResetOptionAlwaysTrueWhenNoLostPasswordLink:

• Asserts canChangePassword is never called ✅
• Asserts userManager->get() called exactly once (not twice as before) ✅
• Asserts canResetPassword is always true ✅

testShowLoginFormLdapUsernameResolutionNotClobbered:

• New test: passes a UUID internal username, asserts loginName resolves to getUserName() ('john.doe'), not the raw UUID ✅
• Directly tests the removed duplicate-block regression ✅

testShowLoginFormCanResetPasswordUniformForNonExistentUser:

• New test: userManager->get() returns null (non-existent user), asserts canResetPassword === true ✅
• This is the key regression guard for the user enumeration fix ✅

testShowLoginFormForUserNamedNull:

• Updated: canChangePassword no longer called, canResetPassword now true ✅

Summary

Aspect	Assessment
User enumeration closed	✅ Backend capability no longer consulted
LDAP name resolution	✅ Duplicate clobbering block removed
Non-existent user indistinguishable	✅ Both paths → canResetPassword=true
Tests	✅ Three new/updated tests directly assert the fix
Changelog	✅ Present

Verdict: Ready to merge.