feat: parse remote address from X-Forwarded-For header

main.go

@@ -7,6 +7,7 @@ import (
 	"net/http/httputil"
 	"net/url"
 	"os"
+	"strings"
 )
 
 func main() {
@@ -34,7 +35,7 @@ func main() {
 		u, p, ok := r.BasicAuth()
 		if !ok || subtle.ConstantTimeCompare([]byte(u), []byte(username)) != 1 ||
 			subtle.ConstantTimeCompare([]byte(p), []byte(password)) != 1 {
-			log.Printf("unauthorized request from %s", r.RemoteAddr)
+			log.Printf("unauthorized request from %s", clientIP(r))
 			w.Header().Set("WWW-Authenticate", `Basic realm="pz8-relay"`)
 			http.Error(w, "unauthorized", http.StatusUnauthorized)
 			return
@@ -46,6 +47,18 @@ func main() {
 	log.Fatal(http.ListenAndServe(addr, nil))
 }
 
+// clientIP returns the original client address, trusting X-Forwarded-For
+// because this service runs behind Traefik. Do not expose directly.
+func clientIP(r *http.Request) string {
+	if xff := r.Header.Get("X-Forwarded-For"); xff != "" {
+		if i := strings.IndexByte(xff, ','); i >= 0 {
+			return strings.TrimSpace(xff[:i])
+		}
+		return strings.TrimSpace(xff)
+	}
+	return r.RemoteAddr
+}
+
 func mustEnv(key string) string {
 	v := os.Getenv(key)
 	if v == "" {