feat: Add Basic Authentication Middleware

Basic Authentication Middleware

This MR adds a complete Basic Authentication middleware implementation for FastAPI.

Features

• ✅ HTTP Basic Authentication support
• ✅ Configurable username/password
• ✅ Path exclusion (for health checks, docs, etc.)
• ✅ Secure constant-time credential comparison
• ✅ Custom authentication realm
• ✅ Comprehensive test coverage
• ✅ Full documentation

Files Added

• middleware/basic_auth.py - Main middleware implementation
• middleware/__init__.py - Package initialization
• tests/test_basic_auth.py - Complete test suite
• middleware/README.md - Usage documentation

Usage Example

from fastapi import FastAPI
from middleware.basic_auth import BasicAuthMiddleware

app = FastAPI()

app.add_middleware(
    BasicAuthMiddleware,
    username="admin",
    password="secret",
    exclude_paths=["/health", "/docs"]
)

Testing

All tests pass:

pytest tests/test_basic_auth.py -v

Security Notes

• Uses secrets.compare_digest() for timing-attack prevention
• Supports path exclusion for public endpoints
• Should be used with HTTPS in production