main.go

package main

import (
	"flag"
	"fmt"
	"net/http"
	"os"
	"strings"

	"github.com/miekg/dns"
	"go.uber.org/zap"
)

var listenAddr = flag.String("listen-addr",
	getEnvDefault("LISTEN_ADDR", ":8080"),
	"local address for serving HTTP (`host:port`)")

func main() {
	flag.Parse()
	logger, err := zap.NewProduction()
	if err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}
	log := logger.Sugar()

	mux := http.NewServeMux()
	mux.HandleFunc("GET /twm/ask", func(w http.ResponseWriter, r *http.Request) {
		log := log.With(
			zap.String("remote_addr", r.RemoteAddr),
			zap.String("request_method", r.Method),
			zap.String("request_path", r.URL.Path),
			zap.String("request_url", r.URL.String()),
			zap.String("xff", r.Header.Get("X-Forwarded-For")),
		)
		domain := r.FormValue("domain")
		log.Info("handle request", "domain", domain)

		// We don't want to tie down names to a specific h-da.cloud
		// project, so accept everything beneath users.h-da.cloud.
		if dns.IsSubDomain("users.h-da.cloud.", strings.TrimSuffix(domain, ".")+".") {
			w.WriteHeader(204)
		}

		// Deny everything else
		w.WriteHeader(403)
	})

	// For readiness/liveliness indication
	readyz := func(w http.ResponseWriter, r *http.Request) {
		w.WriteHeader(200)
	}
	livez := readyz
	mux.HandleFunc("GET /readyz", readyz)
	mux.HandleFunc("GET /livez", livez)

	log.Fatal(
		http.ListenAndServe(*listenAddr, mux),
	)

}

func getEnvDefault(k, def string) string {
	if v := os.Getenv(k); v != "" {
		return v
	}
	return def
}