Fail loudly on half-set metrics auth credentials (closes #205) (#216)

internal/server/routes.go

@@ -55,8 +55,11 @@ func (s *Server) setupGlobalMiddleware() {
 	s.router.Use(s.mw.SecurityHeaders())
 	s.router.Use(s.mw.Logging())
 
-	// Metrics middleware (only if credentials are configured)
-	if s.params.Config.MetricsUsername != "" {
+	// Metrics recording middleware, registered only when the
+	// endpoint that exposes what it records is served. The
+	// condition is the same MetricsAuthEnabled the /metrics mount
+	// in setupRoutes reads.
+	if s.params.Config.MetricsAuthEnabled() {
 		s.router.Use(s.mw.Metrics())
 	}
 
@@ -103,8 +106,14 @@ func (s *Server) setupRoutes() {
 		s.h.HandleHealthCheck(),
 	)
 
-	// set up authenticated /metrics route:
-	if s.params.Config.MetricsUsername != "" {
+	// Authenticated /metrics route. The condition is
+	// Config.MetricsAuthEnabled and never the username alone: a
+	// username with an empty password would otherwise mount the
+	// endpoint behind a credential map that accepts an empty
+	// password. Config rejects that combination at startup, and
+	// this reads the same value the startup log reports, so the
+	// two cannot disagree about whether the route exists.
+	if s.params.Config.MetricsAuthEnabled() {
 		s.router.Group(func(r chi.Router) {
 			r.Use(s.mw.MetricsAuth())
 			r.Get(

internal/server/routes_test.go

@@ -34,6 +34,13 @@ import (
 // the CSRF middleware executed.
 const csrfCookieName = "_gorilla_csrf"
 
+const (
+	// metricsUser and metricsAuthValue are the /metrics basic-auth
+	// credentials the metrics routing tests below configure.
+	metricsUser      = "metrics"
+	metricsAuthValue = "s3cret"
+)
+
 type noopNotifier struct{}
 
 func (n *noopNotifier) Notify([]delivery.Task) {}
@@ -69,9 +76,23 @@ type testEnv struct {
 func newTestEnv(t *testing.T) *testEnv {
 	t.Helper()
 
+	return newTestEnvWithConfig(t, &config.Config{
+		DataDir:     t.TempDir(),
+		Environment: config.EnvironmentDev,
+	})
+}
+
+// newTestEnvWithConfig is newTestEnv over a caller-supplied Config,
+// for the routes whose existence the configuration decides. The same
+// pointer reaches the router and every middleware, so a test cannot
+// accidentally configure one and not the other.
+func newTestEnvWithConfig(
+	t *testing.T, cfg *config.Config,
+) *testEnv {
+	t.Helper()
+
 	var (
 		log   *logger.Logger
-		cfg   *config.Config
 		mw    *middleware.Middleware
 		hnd   *handlers.Handlers
 		sess  *session.Session
@@ -84,12 +105,7 @@ func newTestEnv(t *testing.T) *testEnv {
 		fx.Provide(
 			globals.New,
 			logger.New,
-			func() *config.Config {
-				return &config.Config{
-					DataDir:     t.TempDir(),
-					Environment: config.EnvironmentDev,
-				}
-			},
+			func() *config.Config { return cfg },
 			database.New,
 			database.NewWebhookDBManager,
 			healthcheck.New,
@@ -99,7 +115,7 @@ func newTestEnv(t *testing.T) *testEnv {
 			middleware.New,
 			handlers.New,
 		),
-		fx.Populate(&log, &cfg, &mw, &hnd, &sess, &db, &dbMgr),
+		fx.Populate(&log, &mw, &hnd, &sess, &db, &dbMgr),
 	)
 	app.RequireStart()
 	t.Cleanup(app.RequireStop)
@@ -657,3 +673,119 @@ func TestSourceLogsBody_OtherUser404s(t *testing.T) {
 	assert.Equal(t, http.StatusSeeOther, anon.Code)
 	assert.Equal(t, "/pages/login", anon.Header().Get("Location"))
 }
+
+// metricsConfig is a Config differing from the routing default only
+// in the two /metrics credentials.
+func metricsConfig(
+	t *testing.T, username, password string,
+) *config.Config {
+	t.Helper()
+
+	return &config.Config{
+		DataDir:         t.TempDir(),
+		Environment:     config.EnvironmentDev,
+		MetricsUsername: username,
+		MetricsPassword: password,
+	}
+}
+
+// metricsRequest asks the real router for /metrics with the given
+// basic-auth credentials, or with no Authorization header when
+// username is empty.
+func (e *testEnv) metricsRequest(
+	username, password string,
+) *httptest.ResponseRecorder {
+	req := httptest.NewRequestWithContext(
+		context.Background(), http.MethodGet, "/metrics", nil,
+	)
+
+	if username != "" {
+		req.SetBasicAuth(username, password)
+	}
+
+	w := httptest.NewRecorder()
+	e.router.ServeHTTP(w, req)
+
+	return w
+}
+
+// TestMetricsRouteUnmountedWithoutCredentials pins that with neither
+// credential configured the route does not exist, which is the
+// documented behaviour and the only valid way for /metrics to be
+// absent.
+func TestMetricsRouteUnmountedWithoutCredentials(t *testing.T) {
+	t.Parallel()
+
+	env := newTestEnvWithConfig(t, metricsConfig(t, "", ""))
+
+	assert.Equal(
+		t, http.StatusNotFound,
+		env.metricsRequest("", "").Code,
+	)
+}
+
+// TestMetricsRouteRequiresCredentials pins that with both credentials
+// configured the route exists and every request that does not carry
+// the configured pair is refused — including the empty password that
+// a half-set configuration used to make sufficient.
+func TestMetricsRouteRequiresCredentials(t *testing.T) {
+	t.Parallel()
+
+	env := newTestEnvWithConfig(
+		t, metricsConfig(t, metricsUser, metricsAuthValue),
+	)
+
+	assert.Equal(
+		t, http.StatusUnauthorized,
+		env.metricsRequest("", "").Code,
+		"no credentials must not reach the metrics handler",
+	)
+	assert.Equal(
+		t, http.StatusUnauthorized,
+		env.metricsRequest(metricsUser, "").Code,
+		"an empty password must not reach the metrics handler",
+	)
+	assert.Equal(
+		t, http.StatusUnauthorized,
+		env.metricsRequest(metricsUser, "wrong").Code,
+	)
+
+	ok := env.metricsRequest(metricsUser, metricsAuthValue)
+	assert.Equal(t, http.StatusOK, ok.Code)
+	assert.Contains(t, ok.Body.String(), "go_goroutines")
+}
+
+// TestMetricsRouteUnmountedOnHalfSetConfig pins the defect from
+// https://git.eeqj.de/sneak/webhooker/issues/205 at the routing
+// layer. Config rejects a half-set pair at startup, so this Config
+// cannot be reached from the environment; the assertion is that the
+// route tree does not publish an endpoint accepting an empty
+// password even when handed one anyway, because the mount and the
+// startup log's hasMetricsAuth read the same value.
+func TestMetricsRouteUnmountedOnHalfSetConfig(t *testing.T) {
+	t.Parallel()
+
+	for _, tc := range []struct {
+		name     string
+		username string
+		password string
+	}{
+		{name: "username only", username: metricsUser},
+		{name: "password only", password: metricsAuthValue},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			cfg := metricsConfig(t, tc.username, tc.password)
+			env := newTestEnvWithConfig(t, cfg)
+
+			assert.False(t, cfg.MetricsAuthEnabled())
+			assert.Equal(
+				t, http.StatusNotFound,
+				env.metricsRequest(
+					tc.username, tc.password,
+				).Code,
+			)
+		})
+	}
+}