Cleanup Connection headers before passing the middleware chain

Co-authored-by: Romain <rtribotte@users.noreply.github.com>

pkg/middlewares/auth/connectionheader.go

@@ -0,0 +1,46 @@
+package auth
+
+import (
+	"net/http"
+	"net/textproto"
+	"strings"
+
+	"golang.org/x/net/http/httpguts"
+)
+
+const (
+	connectionHeader = "Connection"
+	upgradeHeader    = "Upgrade"
+)
+
+// Remover removes hop-by-hop headers listed in the "Connection" header.
+// See RFC 7230, section 6.1.
+func Remover(next http.Handler) http.HandlerFunc {
+	return func(rw http.ResponseWriter, req *http.Request) {
+		var reqUpType string
+		if httpguts.HeaderValuesContainsToken(req.Header[connectionHeader], upgradeHeader) {
+			reqUpType = req.Header.Get(upgradeHeader)
+		}
+
+		removeConnectionHeaders(req.Header)
+
+		if reqUpType != "" {
+			req.Header.Set(connectionHeader, upgradeHeader)
+			req.Header.Set(upgradeHeader, reqUpType)
+		} else {
+			req.Header.Del(connectionHeader)
+		}
+
+		next.ServeHTTP(rw, req)
+	}
+}
+
+func removeConnectionHeaders(h http.Header) {
+	for _, f := range h[connectionHeader] {
+		for _, sf := range strings.Split(f, ",") {
+			if sf = textproto.TrimString(sf); sf != "" {
+				h.Del(sf)
+			}
+		}
+	}
+}

pkg/middlewares/auth/connectionheader_test.go

@@ -0,0 +1,70 @@
+package auth
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestRemover(t *testing.T) {
+	testCases := []struct {
+		desc       string
+		reqHeaders map[string]string
+		expected   http.Header
+	}{
+		{
+			desc: "simple remove",
+			reqHeaders: map[string]string{
+				"Foo":            "bar",
+				connectionHeader: "foo",
+			},
+			expected: http.Header{},
+		},
+		{
+			desc: "remove and Upgrade",
+			reqHeaders: map[string]string{
+				upgradeHeader:    "test",
+				"Foo":            "bar",
+				connectionHeader: "Upgrade,foo",
+			},
+			expected: http.Header{
+				upgradeHeader:    []string{"test"},
+				connectionHeader: []string{"Upgrade"},
+			},
+		},
+		{
+			desc: "no remove",
+			reqHeaders: map[string]string{
+				"Foo":            "bar",
+				connectionHeader: "fii",
+			},
+			expected: http.Header{
+				"Foo": []string{"bar"},
+			},
+		},
+	}
+
+	for _, test := range testCases {
+		t.Run(test.desc, func(t *testing.T) {
+			t.Parallel()
+
+			next := http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {})
+
+			h := Remover(next)
+
+			req := httptest.NewRequest(http.MethodGet, "https://localhost", nil)
+
+			for k, v := range test.reqHeaders {
+				req.Header.Set(k, v)
+			}
+
+			rw := httptest.NewRecorder()
+
+			h.ServeHTTP(rw, req)
+
+			assert.Equal(t, test.expected, req.Header)
+		})
+	}
+}

pkg/middlewares/auth/forward.go

@@ -15,7 +15,6 @@ import (
 	"github.com/traefik/traefik/v2/pkg/config/dynamic"
 	"github.com/traefik/traefik/v2/pkg/log"
 	"github.com/traefik/traefik/v2/pkg/middlewares"
-	"github.com/traefik/traefik/v2/pkg/middlewares/connectionheader"
 	"github.com/traefik/traefik/v2/pkg/tracing"
 	"github.com/vulcand/oxy/v2/forward"
 	"github.com/vulcand/oxy/v2/utils"
@@ -90,7 +89,7 @@ func NewForward(ctx context.Context, next http.Handler, config dynamic.ForwardAu
 		fa.authResponseHeadersRegex = re
 	}
 
-	return connectionheader.Remover(fa), nil
+	return Remover(fa), nil
 }
 
 func (fa *forwardAuth) GetTracingInformation() (string, ext.SpanKindEnum) {