Add HTTP authentication support for connectors and listeners

[bearice]

Summary

This PR implements HTTP Basic Authentication support for both HTTP connectors (upstream proxy authentication) and HTTP listeners (client authentication), providing comprehensive authentication capabilities for the redproxy-rs proxy server.

Key Features

🔗 HTTP Connectors (Outbound Authentication)

• New HttpAuthData struct with username and password fields
• Updated HttpConnectorConfig to include optional auth field
• Enhanced http_forward_proxy_connect() to add Proxy-Authorization: Basic <credentials> header
• Full support for both CONNECT tunneling and HTTP forward proxy modes with authentication

🛡️ HTTP Listeners (Inbound Authentication)

• Updated HttpListenerConfig to include AuthData field (following existing SOCKS pattern)
• Enhanced http_forward_proxy_handshake() to parse and validate Proxy-Authorization/Authorization headers
• Integration with existing AuthData validation system (supports both static users and command-based auth)
• Proper error handling with 407 Proxy Authentication Required responses

⚡ QUIC Integration

• Updated QUIC connectors to pass auth parameter (None for backward compatibility)
• Updated QUIC listeners to support authentication using the same AuthData system

Technical Implementation

• HTTP Basic Authentication: Standard Basic <base64(username:password)> encoding
• Robust base64 handling: Proper encoding/decoding with validation and error handling
• Backward compatibility: All auth fields are optional, no breaking changes to existing configs
• Comprehensive testing: Added tests for authentication functionality and base64 operations

Configuration Examples

HTTP Connector with Authentication:

connectors:
  - name: upstream-proxy
    type: http
    server: proxy.example.com
    port: 8080
    auth:
      username: myuser
      password: mypass

HTTP Listener with Authentication:

listeners:
  - name: http-proxy
    type: http
    bind: 0.0.0.0:8080
    auth:
      required: true
      users:
        - username: client1
          password: secret123

Test Plan

• All existing tests pass (71/71)
• New authentication tests added and passing
• Base64 encoding/decoding tests with edge cases
• HTTP connector authentication integration test
• Release build verification completed
• Backward compatibility verified - existing configs work unchanged

Dependencies

• Added base64 crate for proper credential encoding

🤖 Generated with Claude Code