Merge v2.10 into v3.0

pkg/middlewares/headers/header.go

@@ -8,6 +8,7 @@ import (
 	"strings"
 
 	"github.com/traefik/traefik/v3/pkg/config/dynamic"
+	"github.com/vulcand/oxy/v2/forward"
 )
 
 // Header is a middleware that helps setup a few basic security features.
@@ -47,6 +48,7 @@ func NewHeader(next http.Handler, cfg dynamic.Headers) (*Header, error) {
 func (s *Header) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 	// Handle Cors headers and preflight if configured.
 	if isPreflight := s.processCorsHeaders(rw, req); isPreflight {
+		rw.WriteHeader(http.StatusOK)
 		return
 	}
 
@@ -65,6 +67,10 @@ func (s *Header) modifyCustomRequestHeaders(req *http.Request) {
 	// Loop through Custom request headers
 	for header, value := range s.headers.CustomRequestHeaders {
 		switch {
+		// Handling https://github.com/golang/go/commit/ecdbffd4ec68b509998792f120868fec319de59b.
+		case value == "" && header == forward.XForwardedFor:
+			req.Header[header] = nil
+
 		case value == "":
 			req.Header.Del(header)