feat: Support MD5 and SCRAM-SHA-256 password encryption for PostgreSQL connection

[xfg0218]

Overview

This PR adds support for different PostgreSQL password encryption methods (MD5 and SCRAM-SHA-256) to improve compatibility with different PostgreSQL server configurations.

Changes

1. Configuration (internal/config/config.go)

• Added PasswordEncryption field to PostgreSQLConfig struct
• Supports three values: md5, scram-sha-256, auto (default)

2. Connection Manager (internal/postgres/connection.go)

• Modified NewConnection function to append password_encryption parameter to connection string
• Added detailed comments explaining PostgreSQL encryption methods:
  • md5: Traditional encryption, best compatibility
  • scram-sha-256: More secure encryption (PostgreSQL 10+ default)
  • auto: Let PostgreSQL server decide (default behavior)

3. Example Configuration (config.example.yml)

• Added password_encryption: auto configuration example

Motivation

PostgreSQL 10+ uses SCRAM-SHA-256 as the default password encryption method, which is more secure than the traditional MD5 method. However, some environments may still use MD5 for compatibility reasons. This change allows users to explicitly specify which encryption method to use, preventing authentication failures due to encryption method mismatches.

Usage Example

postgresql:
  host: localhost
  port: 5432
  username: postgres
  password: password
  database: test_db
  password_encryption: md5  # or scram-sha-256, or auto (default)

Testing

• Code compiles successfully (go build -o mysql2pg ./cmd/)
• go vet passes without warnings
• Backward compatible (default behavior unchanged when not specified)
• No breaking changes to existing functionality

Related Issue

Closes #110

References

• PostgreSQL Authentication Documentation
• SCRAM-SHA-256 Authentication