Add PostgreSQL and SQLite support via unified SQL backend

[Copilot]

Extends database support from MySQL-only to PostgreSQL and SQLite while maintaining full backward compatibility. Implements a driver abstraction layer allowing users to switch databases via configuration.

Implementation

Driver Abstraction

• BaseSqlDriver: Interface defining common operations (connect, query, findUser, etc.)
• SqlDriverFactory: Creates appropriate driver based on SQL_DRIVER config
• Automatic placeholder conversion (? → $1, $2 for PostgreSQL)
• Custom query support via SQL_QUERY_* environment variables

Drivers

• MySQLDriver: Refactored existing implementation to extend base class
• PostgreSQLDriver: JSONB support with ? operator for array membership
• SQLiteDriver: JSON1 extension for JSON operations

Generic Backends

• sql.auth.js / sql.directory.js: Dialect-agnostic backends using factory pattern
• Legacy mysql.auth.js / mysql.directory.js unchanged for rollback safety

Configuration

# New unified configuration
SQL_DRIVER=postgresql          # mysql | postgresql | sqlite
SQL_HOST=localhost
SQL_PORT=5432
SQL_DATABASE=ldap_db

# Legacy MYSQL_* variables still work
MYSQL_HOST=localhost           # Backward compatible

Migration

Existing deployments continue working unchanged. To use new backend:

- AUTH_BACKENDS=mysql
+ AUTH_BACKENDS=sql
+ SQL_DRIVER=mysql
  MYSQL_HOST=localhost          # Still supported

Rollback requires only reverting backend name.

Schema

Identical logical schema across all dialects. Initialization scripts provided for each:

• MySQL: docker/sql/init.sql
• PostgreSQL: docker/sql/init-postgresql.sql
• SQLite: docker/sql/init-sqlite.sql

Testing

• 29 unit tests covering driver abstraction and factory
• 3 integration tests for connectivity
• CodeQL: 0 vulnerabilities

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Support Multiple SQL Dialects</issue_title>
<issue_description>We are looking to support SQLite3 and PostgreSQL in addition to MySQL. I would like to accomplish this by refitting the MySQL Directory and Authentication backends to be more generically named SQL (ie. SQL_HOST, SQL_USER, SQL_DATABASE, SQL_PASSWORD, SQL_SCHEMA etc). We then need an abstraction layer to select the right database driver for the configured SQL_DRIVER. The user could then supply the required SQL queries as additional configuration parameters.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Support Multiple SQL Dialects #102

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[runleveldev]

implemented in #104