Rate Limiter: Add Trusted Proxy Configuration for X-Forwarded-For Support

[bupd]

Problem

The rate limiter in ground-control/internal/middleware/ratelimit.go currently only uses r.RemoteAddr for client identification and ignores X-Forwarded-For headers. While this is secure against IP spoofing, it becomes problematic when Ground Control runs behind a reverse proxy (nginx, AWS ALB, K8s Ingress).

When behind a proxy, all requests appear to come from the proxy's IP, causing all clients to share the same rate limit bucket.

Current Behavior

func getClientIP(r *http.Request) string {
    // Only use RemoteAddr - ignores X-Forwarded-For
    host, _, err := net.SplitHostPort(r.RemoteAddr)
    // ...
}

Proposed Solution

Add configuration for trusted proxies:

1. Add TrustedProxies []string configuration option
2. Only parse X-Forwarded-For when the immediate client is in the trusted list
3. Validate the header chain to prevent spoofing

Reference

• File: ground-control/internal/middleware/ratelimit.go:106-115