composing.go

package main

import "net/http"

func main() {
	http.HandleFunc("/", publicHandler)
	http.HandleFunc("/admin", authenticate(adminHandler))

	http.ListenAndServe(":8080", nil)
}

func authenticate(h http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		user, pass, ok := r.BasicAuth()
		if ok && user == "john" && pass == "secret" {
			h.ServeHTTP(w, r)
			return
		}

		w.WriteHeader(http.StatusUnauthorized)
	}
}

func publicHandler(w http.ResponseWriter, r *http.Request) {
	w.Write([]byte("public"))
}

func adminHandler(w http.ResponseWriter, r *http.Request) {
	w.Write([]byte("admin"))
}