fix(auth): allow zero string credentials

[tbasten]

Summary

Fixes authentication credential validation so string "0" is treated as a valid non-empty username or password.

Previously Guard::attempt() used PHP empty() checks. In PHP, empty("0") === true, so a password or username of "0" incorrectly triggered UsernameRequiredException / PasswordRequiredException instead of attempting LDAP bind.

Changes

• Replace empty($username) with $username === ''
• Replace empty($password) with $password === ''
• Add regression coverage for:
  • password "0"
  • username "0"

Why

A zero 0 string is not an empty credential. Applications using validation rules such as Laravel’s required|string accept "0" as present, but LdapRecord rejected it as missing. This caused valid input to be treated as absent before LDAP bind was attempted.

Validation

• ./vendor/bin/phpunit --filter='test_attempt_allows_zero_string'
• ./vendor/bin/phpunit tests/Unit/Auth/GuardTest.php
• ./vendor/bin/pint --dirty

Targeted auth tests pass. Full suite was not run locally because the PHP LDAP extension/constants are unavailable in my local environment.

[Copilot]

🟢 Approval recommended

The change precisely addresses PHP empty("0") behavior and includes targeted regression tests for both username and password cases.

Pull request overview

This PR fixes LDAP authentication credential validation so the string "0" is treated as a valid (non-empty) username/password, avoiding PHP empty() semantics that incorrectly classify "0" as empty.

Changes:

• Update Guard::attempt() to validate credentials with strict empty-string checks (=== '') instead of empty().
• Add unit-test regression coverage for "0" username and "0" password in GuardTest.

File summaries

File	Description
src/Auth/Guard.php	Adjusts credential validation to accept "0" as a valid string and proceed to bind.
tests/Unit/Auth/GuardTest.php	Adds regression tests ensuring "0" credentials are accepted and binding proceeds as expected.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Lite

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[stevebauman]

Thanks @tbasten! Created release v4.0.7 with this patch.