basicauth: log warning on healthz (#1039)

* basicauth: log warning on healthz

* include http path prefix

cmd/proxy/actions/basicauth.go

@@ -3,14 +3,26 @@ package actions
 import (
 	"crypto/subtle"
 	"net/http"
+	"strings"
 
+	"github.com/gomods/athens/pkg/log"
 	"github.com/gorilla/mux"
 )
 
+const healthWarning = "/healthz received none or incorrect Basic-Auth headers"
+
 func basicAuth(user, pass string) mux.MiddlewareFunc {
 	return func(h http.Handler) http.Handler {
 		f := func(w http.ResponseWriter, r *http.Request) {
 			if !checkAuth(r, user, pass) {
+				// Helpful hint for Kubernetes users:
+				// if they forget to send auth headers
+				// kubernetes silently fails, so a log
+				// might help them.
+				if strings.HasSuffix(r.URL.Path, "/healthz") {
+					lggr := log.EntryFromContext(r.Context())
+					lggr.Warnf(healthWarning)
+				}
 				w.Header().Set("WWW-Authenticate", `Basic realm="basic auth required"`)
 				w.WriteHeader(http.StatusUnauthorized)
 				return