Как спроектировать API gateway на Go?

Reverse proxy с middleware: auth (JWT validation), rate limiting, request/response transformation, routing, load balancing. Конфигурация: YAML/JSON с hot reload. Middleware chain через http.Handler wrapping. Health checks для backends. Circuit breaker per backend. Метрики: latency, error rate per route. Go: net/http/httputil.ReverseProxy как основа, custom Director function.