fix(tracing): makes sure tracing headers are being propagated when using forwardAuth

pkg/middlewares/auth/forward.go

@@ -88,9 +88,11 @@ func (fa *forwardAuth) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 		return
 	}
 
-	writeHeader(req, forwardReq, fa.trustForwardHeader)
+	// Ensure tracing headers are in the request before we copy the headers to the
+	// forwardReq.
+	tracing.InjectRequestHeaders(req)
 
-	tracing.InjectRequestHeaders(forwardReq)
+	writeHeader(req, forwardReq, fa.trustForwardHeader)
 
 	forwardResponse, forwardErr := httpClient.Do(forwardReq)
 	if forwardErr != nil {

pkg/middlewares/auth/forward_test.go

@@ -3,13 +3,18 @@ package auth
 import (
 	"context"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"net/http"
 	"net/http/httptest"
 	"testing"
 
 	"github.com/containous/traefik/v2/pkg/config/dynamic"
+	tracingMiddleware "github.com/containous/traefik/v2/pkg/middlewares/tracing"
 	"github.com/containous/traefik/v2/pkg/testhelpers"
+	"github.com/containous/traefik/v2/pkg/tracing"
+	"github.com/opentracing/opentracing-go"
+	"github.com/opentracing/opentracing-go/mocktracer"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"github.com/vulcand/oxy/forward"
@@ -394,3 +399,44 @@ func Test_writeHeader(t *testing.T) {
 		})
 	}
 }
+
+func TestForwardAuthUsesTracing(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Header.Get("Mockpfx-Ids-Traceid") == "" {
+			t.Errorf("expected Mockpfx-Ids-Traceid header to be present in request")
+		}
+	}))
+	defer server.Close()
+
+	next := http.Handler(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {}))
+
+	auth := dynamic.ForwardAuth{
+		Address: server.URL,
+	}
+
+	tracer := mocktracer.New()
+	opentracing.SetGlobalTracer(tracer)
+
+	tr, _ := tracing.NewTracing("testApp", 100, &mockBackend{tracer})
+
+	next, err := NewForward(context.Background(), next, auth, "authTest")
+	require.NoError(t, err)
+
+	next = tracingMiddleware.NewEntryPoint(context.Background(), tr, "tracingTest", next)
+
+	ts := httptest.NewServer(next)
+	defer ts.Close()
+
+	req := testhelpers.MustNewRequest(http.MethodGet, ts.URL, nil)
+	res, err := http.DefaultClient.Do(req)
+	require.NoError(t, err)
+	assert.Equal(t, http.StatusOK, res.StatusCode)
+}
+
+type mockBackend struct {
+	opentracing.Tracer
+}
+
+func (b *mockBackend) Setup(componentName string) (opentracing.Tracer, io.Closer, error) {
+	return b.Tracer, ioutil.NopCloser(nil), nil
+}