Do not copy hop-by-hop headers to forward auth request

middlewares/auth/forward.go

@@ -105,6 +105,7 @@ func Forward(config *types.Forward, w http.ResponseWriter, r *http.Request, next
 
 func writeHeader(req *http.Request, forwardReq *http.Request, trustForwardHeader bool) {
 	utils.CopyHeaders(forwardReq.Header, req.Header)
+	utils.RemoveHeaders(forwardReq.Header, forward.HopHeaders...)
 
 	if clientIP, _, err := net.SplitHostPort(req.RemoteAddr); err == nil {
 		if trustForwardHeader {

middlewares/auth/forward_test.go

@@ -231,11 +231,12 @@ func TestForwardAuthFailResponseHeaders(t *testing.T) {
 
 func Test_writeHeader(t *testing.T) {
 	testCases := []struct {
-		name               string
-		headers            map[string]string
-		trustForwardHeader bool
-		emptyHost          bool
-		expectedHeaders    map[string]string
+		name                      string
+		headers                   map[string]string
+		trustForwardHeader        bool
+		emptyHost                 bool
+		expectedHeaders           map[string]string
+		checkForUnexpectedHeaders bool
 	}{
 		{
 			name: "trust Forward Header",
@@ -334,6 +335,29 @@ func Test_writeHeader(t *testing.T) {
 				"X-Forwarded-Method": "GET",
 			},
 		},
+		{
+			name: "remove hop-by-hop headers",
+			headers: map[string]string{
+				forward.Connection:         "Connection",
+				forward.KeepAlive:          "KeepAlive",
+				forward.ProxyAuthenticate:  "ProxyAuthenticate",
+				forward.ProxyAuthorization: "ProxyAuthorization",
+				forward.Te:                 "Te",
+				forward.Trailers:           "Trailers",
+				forward.TransferEncoding:   "TransferEncoding",
+				forward.Upgrade:            "Upgrade",
+				"X-CustomHeader":           "CustomHeader",
+			},
+			trustForwardHeader: false,
+			expectedHeaders: map[string]string{
+				"X-CustomHeader":     "CustomHeader",
+				"X-Forwarded-Proto":  "http",
+				"X-Forwarded-Host":   "foo.bar",
+				"X-Forwarded-Uri":    "/path?q=1",
+				"X-Forwarded-Method": "GET",
+			},
+			checkForUnexpectedHeaders: true,
+		},
 	}
 
 	for _, test := range testCases {
@@ -352,8 +376,16 @@ func Test_writeHeader(t *testing.T) {
 
 			writeHeader(req, forwardReq, test.trustForwardHeader)
 
-			for key, value := range test.expectedHeaders {
-				assert.Equal(t, value, forwardReq.Header.Get(key))
+			actualHeaders := forwardReq.Header
+			expectedHeaders := test.expectedHeaders
+			for key, value := range expectedHeaders {
+				assert.Equal(t, value, actualHeaders.Get(key))
+				actualHeaders.Del(key)
+			}
+			if test.checkForUnexpectedHeaders {
+				for key := range actualHeaders {
+					assert.Fail(t, "Unexpected header found", key)
+				}
 			}
 		})
 	}