hscontrol: log acme/autocert errors (#2933)

hscontrol/app.go

@@ -5,6 +5,7 @@ import (
 	"crypto/tls"
 	"errors"
 	"fmt"
+	"io"
 	"net"
 	"net/http"
 	_ "net/http/pprof" // nolint
@@ -877,6 +878,11 @@ func (h *Headscale) getTLSSettings() (*tls.Config, error) {
 			Cache:      autocert.DirCache(h.cfg.TLS.LetsEncrypt.CacheDir),
 			Client: &acme.Client{
 				DirectoryURL: h.cfg.ACMEURL,
+				HTTPClient: &http.Client{
+					Transport: &acmeLogger{
+						rt: http.DefaultTransport,
+					},
+				},
 			},
 			Email: h.cfg.ACMEEmail,
 		}
@@ -997,3 +1003,28 @@ func readOrCreatePrivateKey(path string) (*key.MachinePrivate, error) {
 func (h *Headscale) Change(cs ...change.ChangeSet) {
 	h.mapBatcher.AddWork(cs...)
 }
+
+// Provide some middleware that can inspect the ACME/autocert https calls
+// and log when things are failing.
+type acmeLogger struct {
+	rt http.RoundTripper
+}
+
+// RoundTrip will log when ACME/autocert failures happen either when err != nil OR
+// when http status codes indicate a failure has occurred.
+func (l *acmeLogger) RoundTrip(req *http.Request) (*http.Response, error) {
+	resp, err := l.rt.RoundTrip(req)
+	if err != nil {
+		log.Error().Err(err).Str("url", req.URL.String()).Msg("ACME request failed")
+		return nil, err
+	}
+
+	if resp.StatusCode >= http.StatusBadRequest {
+		defer resp.Body.Close()
+
+		body, _ := io.ReadAll(resp.Body)
+		log.Error().Int("status_code", resp.StatusCode).Str("url", req.URL.String()).Bytes("body", body).Msg("ACME request returned error")
+	}
+
+	return resp, nil
+}