Support ResponseHeaderModifier filter

integration/k8s_conformance_test.go

@@ -86,8 +86,8 @@ func (s *K8sConformanceSuite) SetupSuite() {
 		s.T().Fatal("Traefik image is not present")
 	}
 
-	s.k3sContainer, err = k3s.RunContainer(ctx,
+	s.k3sContainer, err = k3s.Run(ctx,
-		testcontainers.WithImage(k3sImage),
+		k3sImage,
 		k3s.WithManifest("./fixtures/k8s-conformance/00-experimental-v1.1.0.yml"),
 		k3s.WithManifest("./fixtures/k8s-conformance/01-rbac.yml"),
 		k3s.WithManifest("./fixtures/k8s-conformance/02-traefik.yml"),
@@ -206,6 +206,7 @@ func (s *K8sConformanceSuite) TestK8sGatewayAPIConformance() {
 			features.SupportHTTPRouteHostRewrite,
 			features.SupportHTTPRoutePathRewrite,
 			features.SupportHTTPRoutePathRedirect,
+			features.SupportHTTPRouteResponseHeaderModification,
 		),
 	})
 	require.NoError(s.T(), err)

pkg/config/dynamic/middlewares.go

@@ -40,8 +40,9 @@ type Middleware struct {
 
 	Plugin map[string]PluginConf `json:"plugin,omitempty" toml:"plugin,omitempty" yaml:"plugin,omitempty" export:"true"`
 
-	// Gateway API HTTPRoute filters middlewares.
+	// Gateway API filter middlewares.
-	RequestHeaderModifier *RequestHeaderModifier `json:"requestHeaderModifier,omitempty" toml:"-" yaml:"-" label:"-" file:"-" kv:"-" export:"true"`
+	RequestHeaderModifier  *HeaderModifier  `json:"requestHeaderModifier,omitempty" toml:"-" yaml:"-" label:"-" file:"-" kv:"-" export:"true"`
+	ResponseHeaderModifier *HeaderModifier  `json:"responseHeaderModifier,omitempty" toml:"-" yaml:"-" label:"-" file:"-" kv:"-" export:"true"`
 	RequestRedirect        *RequestRedirect `json:"requestRedirect,omitempty" toml:"-" yaml:"-" label:"-" file:"-" kv:"-" export:"true"`
 	URLRewrite             *URLRewrite      `json:"URLRewrite,omitempty" toml:"-" yaml:"-" label:"-" file:"-" kv:"-" export:"true"`
 }
@@ -694,8 +695,8 @@ type Users []string
 
 // +k8s:deepcopy-gen=true
 
-// RequestHeaderModifier holds the request header modifier configuration.
+// HeaderModifier holds the request/response header modifier configuration.
-type RequestHeaderModifier struct {
+type HeaderModifier struct {
 	Set    map[string]string `json:"set,omitempty"`
 	Add    map[string]string `json:"add,omitempty"`
 	Remove []string          `json:"remove,omitempty"`

pkg/config/dynamic/zz_generated.deepcopy.go

@@ -506,6 +506,41 @@ func (in *HTTPConfiguration) DeepCopy() *HTTPConfiguration {
 	return out
 }
 
+// DeepCopyInto is an autogenerated deepcopy function, copying the receiver, writing into out. in must be non-nil.
+func (in *HeaderModifier) DeepCopyInto(out *HeaderModifier) {
+	*out = *in
+	if in.Set != nil {
+		in, out := &in.Set, &out.Set
+		*out = make(map[string]string, len(*in))
+		for key, val := range *in {
+			(*out)[key] = val
+		}
+	}
+	if in.Add != nil {
+		in, out := &in.Add, &out.Add
+		*out = make(map[string]string, len(*in))
+		for key, val := range *in {
+			(*out)[key] = val
+		}
+	}
+	if in.Remove != nil {
+		in, out := &in.Remove, &out.Remove
+		*out = make([]string, len(*in))
+		copy(*out, *in)
+	}
+	return
+}
+
+// DeepCopy is an autogenerated deepcopy function, copying the receiver, creating a new HeaderModifier.
+func (in *HeaderModifier) DeepCopy() *HeaderModifier {
+	if in == nil {
+		return nil
+	}
+	out := new(HeaderModifier)
+	in.DeepCopyInto(out)
+	return out
+}
+
 // DeepCopyInto is an autogenerated deepcopy function, copying the receiver, writing into out. in must be non-nil.
 func (in *Headers) DeepCopyInto(out *Headers) {
 	*out = *in
@@ -866,7 +901,12 @@ func (in *Middleware) DeepCopyInto(out *Middleware) {
 	}
 	if in.RequestHeaderModifier != nil {
 		in, out := &in.RequestHeaderModifier, &out.RequestHeaderModifier
-		*out = new(RequestHeaderModifier)
+		*out = new(HeaderModifier)
+		(*in).DeepCopyInto(*out)
+	}
+	if in.ResponseHeaderModifier != nil {
+		in, out := &in.ResponseHeaderModifier, &out.ResponseHeaderModifier
+		*out = new(HeaderModifier)
 		(*in).DeepCopyInto(*out)
 	}
 	if in.RequestRedirect != nil {
@@ -1087,41 +1127,6 @@ func (in *ReplacePathRegex) DeepCopy() *ReplacePathRegex {
 	return out
 }
 
-// DeepCopyInto is an autogenerated deepcopy function, copying the receiver, writing into out. in must be non-nil.
-func (in *RequestHeaderModifier) DeepCopyInto(out *RequestHeaderModifier) {
-	*out = *in
-	if in.Set != nil {
-		in, out := &in.Set, &out.Set
-		*out = make(map[string]string, len(*in))
-		for key, val := range *in {
-			(*out)[key] = val
-		}
-	}
-	if in.Add != nil {
-		in, out := &in.Add, &out.Add
-		*out = make(map[string]string, len(*in))
-		for key, val := range *in {
-			(*out)[key] = val
-		}
-	}
-	if in.Remove != nil {
-		in, out := &in.Remove, &out.Remove
-		*out = make([]string, len(*in))
-		copy(*out, *in)
-	}
-	return
-}
-
-// DeepCopy is an autogenerated deepcopy function, copying the receiver, creating a new RequestHeaderModifier.
-func (in *RequestHeaderModifier) DeepCopy() *RequestHeaderModifier {
-	if in == nil {
-		return nil
-	}
-	out := new(RequestHeaderModifier)
-	in.DeepCopyInto(out)
-	return out
-}
-
 // DeepCopyInto is an autogenerated deepcopy function, copying the receiver, writing into out. in must be non-nil.
 func (in *RequestRedirect) DeepCopyInto(out *RequestRedirect) {
 	*out = *in

pkg/middlewares/gatewayapi/headermodifier/request_header_modifier.go

@@ -9,7 +9,7 @@ import (
 	"go.opentelemetry.io/otel/trace"
 )
 
-const typeName = "RequestHeaderModifier"
+const requestHeaderModifierTypeName = "RequestHeaderModifier"
 
 // requestHeaderModifier is a middleware used to modify the headers of an HTTP request.
 type requestHeaderModifier struct {
@@ -22,8 +22,8 @@ type requestHeaderModifier struct {
 }
 
 // NewRequestHeaderModifier creates a new request header modifier middleware.
-func NewRequestHeaderModifier(ctx context.Context, next http.Handler, config dynamic.RequestHeaderModifier, name string) http.Handler {
+func NewRequestHeaderModifier(ctx context.Context, next http.Handler, config dynamic.HeaderModifier, name string) http.Handler {
-	logger := middlewares.GetLogger(ctx, name, typeName)
+	logger := middlewares.GetLogger(ctx, name, requestHeaderModifierTypeName)
 	logger.Debug().Msg("Creating middleware")
 
 	return &requestHeaderModifier{
@@ -36,7 +36,7 @@ func NewRequestHeaderModifier(ctx context.Context, next http.Handler, config dyn
 }
 
 func (r *requestHeaderModifier) GetTracingInformation() (string, string, trace.SpanKind) {
-	return r.name, typeName, trace.SpanKindUnspecified
+	return r.name, requestHeaderModifierTypeName, trace.SpanKindUnspecified
 }
 
 func (r *requestHeaderModifier) ServeHTTP(rw http.ResponseWriter, req *http.Request) {

pkg/middlewares/gatewayapi/headermodifier/request_header_modifier_test.go

@@ -14,25 +14,25 @@ import (
 func TestRequestHeaderModifier(t *testing.T) {
 	testCases := []struct {
 		desc            string
-		config          dynamic.RequestHeaderModifier
+		config          dynamic.HeaderModifier
 		requestHeaders  http.Header
 		expectedHeaders http.Header
 	}{
 		{
 			desc:            "no config",
-			config:          dynamic.RequestHeaderModifier{},
+			config:          dynamic.HeaderModifier{},
 			expectedHeaders: map[string][]string{},
 		},
 		{
 			desc: "set header",
-			config: dynamic.RequestHeaderModifier{
+			config: dynamic.HeaderModifier{
 				Set: map[string]string{"Foo": "Bar"},
 			},
 			expectedHeaders: map[string][]string{"Foo": {"Bar"}},
 		},
 		{
 			desc: "set header with existing headers",
-			config: dynamic.RequestHeaderModifier{
+			config: dynamic.HeaderModifier{
 				Set: map[string]string{"Foo": "Bar"},
 			},
 			requestHeaders:  map[string][]string{"Foo": {"Baz"}, "Bar": {"Foo"}},
@@ -40,7 +40,7 @@ func TestRequestHeaderModifier(t *testing.T) {
 		},
 		{
 			desc: "set multiple headers with existing headers",
-			config: dynamic.RequestHeaderModifier{
+			config: dynamic.HeaderModifier{
 				Set: map[string]string{"Foo": "Bar", "Bar": "Foo"},
 			},
 			requestHeaders:  map[string][]string{"Foo": {"Baz"}, "Bar": {"Foobar"}},
@@ -48,14 +48,14 @@ func TestRequestHeaderModifier(t *testing.T) {
 		},
 		{
 			desc: "add header",
-			config: dynamic.RequestHeaderModifier{
+			config: dynamic.HeaderModifier{
 				Add: map[string]string{"Foo": "Bar"},
 			},
 			expectedHeaders: map[string][]string{"Foo": {"Bar"}},
 		},
 		{
 			desc: "add header with existing headers",
-			config: dynamic.RequestHeaderModifier{
+			config: dynamic.HeaderModifier{
 				Add: map[string]string{"Foo": "Bar"},
 			},
 			requestHeaders:  map[string][]string{"Foo": {"Baz"}, "Bar": {"Foo"}},
@@ -63,7 +63,7 @@ func TestRequestHeaderModifier(t *testing.T) {
 		},
 		{
 			desc: "add multiple headers with existing headers",
-			config: dynamic.RequestHeaderModifier{
+			config: dynamic.HeaderModifier{
 				Add: map[string]string{"Foo": "Bar", "Bar": "Foo"},
 			},
 			requestHeaders:  map[string][]string{"Foo": {"Baz"}, "Bar": {"Foobar"}},
@@ -71,14 +71,14 @@ func TestRequestHeaderModifier(t *testing.T) {
 		},
 		{
 			desc: "remove header",
-			config: dynamic.RequestHeaderModifier{
+			config: dynamic.HeaderModifier{
 				Remove: []string{"Foo"},
 			},
 			expectedHeaders: map[string][]string{},
 		},
 		{
 			desc: "remove header with existing headers",
-			config: dynamic.RequestHeaderModifier{
+			config: dynamic.HeaderModifier{
 				Remove: []string{"Foo"},
 			},
 			requestHeaders:  map[string][]string{"Foo": {"Baz"}, "Bar": {"Foo"}},
@@ -86,7 +86,7 @@ func TestRequestHeaderModifier(t *testing.T) {
 		},
 		{
 			desc: "remove multiple headers with existing headers",
-			config: dynamic.RequestHeaderModifier{
+			config: dynamic.HeaderModifier{
 				Remove: []string{"Foo", "Bar"},
 			},
 			requestHeaders:  map[string][]string{"Foo": {"Bar"}, "Bar": {"Foo"}, "Baz": {"Bar"}},
@@ -106,11 +106,11 @@ func TestRequestHeaderModifier(t *testing.T) {
 			handler := NewRequestHeaderModifier(context.Background(), next, test.config, "foo-request-header-modifier")
 
 			req := testhelpers.MustNewRequest(http.MethodGet, "http://localhost", nil)
-			if test.requestHeaders != nil {
+			for h, v := range test.requestHeaders {
-				req.Header = test.requestHeaders
+				req.Header[h] = v
 			}
-
 			resp := httptest.NewRecorder()
+
 			handler.ServeHTTP(resp, req)
 
 			assert.Equal(t, test.expectedHeaders, gotHeaders)

pkg/middlewares/gatewayapi/headermodifier/response_header_modifier.go

@@ -0,0 +1,60 @@
+package headermodifier
+
+import (
+	"context"
+	"net/http"
+
+	"github.com/traefik/traefik/v3/pkg/config/dynamic"
+	"github.com/traefik/traefik/v3/pkg/middlewares"
+	"go.opentelemetry.io/otel/trace"
+)
+
+const responseHeaderModifierTypeName = "ResponseHeaderModifier"
+
+// requestHeaderModifier is a middleware used to modify the headers of an HTTP response.
+type responseHeaderModifier struct {
+	next http.Handler
+	name string
+
+	set    map[string]string
+	add    map[string]string
+	remove []string
+}
+
+// NewResponseHeaderModifier creates a new response header modifier middleware.
+func NewResponseHeaderModifier(ctx context.Context, next http.Handler, config dynamic.HeaderModifier, name string) http.Handler {
+	logger := middlewares.GetLogger(ctx, name, responseHeaderModifierTypeName)
+	logger.Debug().Msg("Creating middleware")
+
+	return &responseHeaderModifier{
+		next:   next,
+		name:   name,
+		set:    config.Set,
+		add:    config.Add,
+		remove: config.Remove,
+	}
+}
+
+func (r *responseHeaderModifier) GetTracingInformation() (string, string, trace.SpanKind) {
+	return r.name, responseHeaderModifierTypeName, trace.SpanKindUnspecified
+}
+
+func (r *responseHeaderModifier) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
+	r.next.ServeHTTP(middlewares.NewResponseModifier(rw, req, r.modifyResponseHeaders), req)
+}
+
+func (r *responseHeaderModifier) modifyResponseHeaders(res *http.Response) error {
+	for headerName, headerValue := range r.set {
+		res.Header.Set(headerName, headerValue)
+	}
+
+	for headerName, headerValue := range r.add {
+		res.Header.Add(headerName, headerValue)
+	}
+
+	for _, headerName := range r.remove {
+		res.Header.Del(headerName)
+	}
+
+	return nil
+}

pkg/middlewares/gatewayapi/headermodifier/response_header_modifier_test.go

@@ -0,0 +1,121 @@
+package headermodifier
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/traefik/traefik/v3/pkg/config/dynamic"
+	"github.com/traefik/traefik/v3/pkg/testhelpers"
+)
+
+func TestResponseHeaderModifier(t *testing.T) {
+	testCases := []struct {
+		desc            string
+		config          dynamic.HeaderModifier
+		responseHeaders http.Header
+		expectedHeaders http.Header
+	}{
+		{
+			desc:            "no config",
+			config:          dynamic.HeaderModifier{},
+			expectedHeaders: map[string][]string{},
+		},
+		{
+			desc: "set header",
+			config: dynamic.HeaderModifier{
+				Set: map[string]string{"Foo": "Bar"},
+			},
+			expectedHeaders: map[string][]string{"Foo": {"Bar"}},
+		},
+		{
+			desc: "set header with existing headers",
+			config: dynamic.HeaderModifier{
+				Set: map[string]string{"Foo": "Bar"},
+			},
+			responseHeaders: map[string][]string{"Foo": {"Baz"}, "Bar": {"Foo"}},
+			expectedHeaders: map[string][]string{"Foo": {"Bar"}, "Bar": {"Foo"}},
+		},
+		{
+			desc: "set multiple headers with existing headers",
+			config: dynamic.HeaderModifier{
+				Set: map[string]string{"Foo": "Bar", "Bar": "Foo"},
+			},
+			responseHeaders: map[string][]string{"Foo": {"Baz"}, "Bar": {"Foobar"}},
+			expectedHeaders: map[string][]string{"Foo": {"Bar"}, "Bar": {"Foo"}},
+		},
+		{
+			desc: "add header",
+			config: dynamic.HeaderModifier{
+				Add: map[string]string{"Foo": "Bar"},
+			},
+			expectedHeaders: map[string][]string{"Foo": {"Bar"}},
+		},
+		{
+			desc: "add header with existing headers",
+			config: dynamic.HeaderModifier{
+				Add: map[string]string{"Foo": "Bar"},
+			},
+			responseHeaders: map[string][]string{"Foo": {"Baz"}, "Bar": {"Foo"}},
+			expectedHeaders: map[string][]string{"Foo": {"Baz", "Bar"}, "Bar": {"Foo"}},
+		},
+		{
+			desc: "add multiple headers with existing headers",
+			config: dynamic.HeaderModifier{
+				Add: map[string]string{"Foo": "Bar", "Bar": "Foo"},
+			},
+			responseHeaders: map[string][]string{"Foo": {"Baz"}, "Bar": {"Foobar"}},
+			expectedHeaders: map[string][]string{"Foo": {"Baz", "Bar"}, "Bar": {"Foobar", "Foo"}},
+		},
+		{
+			desc: "remove header",
+			config: dynamic.HeaderModifier{
+				Remove: []string{"Foo"},
+			},
+			expectedHeaders: map[string][]string{},
+		},
+		{
+			desc: "remove header with existing headers",
+			config: dynamic.HeaderModifier{
+				Remove: []string{"Foo"},
+			},
+			responseHeaders: map[string][]string{"Foo": {"Baz"}, "Bar": {"Foo"}},
+			expectedHeaders: map[string][]string{"Bar": {"Foo"}},
+		},
+		{
+			desc: "remove multiple headers with existing headers",
+			config: dynamic.HeaderModifier{
+				Remove: []string{"Foo", "Bar"},
+			},
+			responseHeaders: map[string][]string{"Foo": {"Bar"}, "Bar": {"Foo"}, "Baz": {"Bar"}},
+			expectedHeaders: map[string][]string{"Baz": {"Bar"}},
+		},
+	}
+
+	for _, test := range testCases {
+		t.Run(test.desc, func(t *testing.T) {
+			t.Parallel()
+
+			var nextCallCount int
+			next := http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+				nextCallCount++
+				rw.WriteHeader(http.StatusOK)
+			})
+
+			handler := NewResponseHeaderModifier(context.Background(), next, test.config, "foo-response-header-modifier")
+
+			req := testhelpers.MustNewRequest(http.MethodGet, "http://localhost", nil)
+			resp := httptest.NewRecorder()
+			for k, v := range test.responseHeaders {
+				resp.Header()[k] = v
+			}
+
+			handler.ServeHTTP(resp, req)
+
+			assert.Equal(t, 1, nextCallCount)
+			assert.Equal(t, test.expectedHeaders, resp.Header())
+		})
+	}
+}

pkg/middlewares/gatewayapi/redirect/request_redirect.go

@@ -13,9 +13,7 @@ import (
 	"go.opentelemetry.io/otel/trace"
 )
 
-const (
+const typeName = "RequestRedirect"
-	typeName = "RequestRedirect"
-)
 
 type redirect struct {
 	name string

pkg/provider/kubernetes/gateway/fixtures/httproute/filter_response_header_modifier.yml

@@ -0,0 +1,62 @@
+---
+kind: GatewayClass
+apiVersion: gateway.networking.k8s.io/v1
+metadata:
+  name: my-gateway-class
+spec:
+  controllerName: traefik.io/gateway-controller
+
+---
+kind: Gateway
+apiVersion: gateway.networking.k8s.io/v1
+metadata:
+  name: my-gateway
+  namespace: default
+spec:
+  gatewayClassName: my-gateway-class
+  listeners: # Use GatewayClass defaults for listener definition.
+    - name: http
+      protocol: HTTP
+      port: 80
+      allowedRoutes:
+        kinds:
+          - kind: HTTPRoute
+            group: gateway.networking.k8s.io
+        namespaces:
+          from: Same
+
+---
+kind: HTTPRoute
+apiVersion: gateway.networking.k8s.io/v1
+metadata:
+  name: http-app-1
+  namespace: default
+spec:
+  parentRefs:
+    - name: my-gateway
+      kind: Gateway
+      group: gateway.networking.k8s.io
+  hostnames:
+    - "example.org"
+  rules:
+    - matches:
+        - path:
+            type: PathPrefix
+            value: /
+      backendRefs:
+        - name: whoami
+          port: 80
+          weight: 1
+          kind: Service
+          group: ""
+      filters:
+        - type: ResponseHeaderModifier
+          responseHeaderModifier:
+            set:
+              - name: X-Foo
+                value: Bar
+            add:
+              - name: X-Bar
+                value: Foo
+            remove:
+              - X-Baz

pkg/provider/kubernetes/gateway/httproute.go

@@ -316,6 +316,9 @@ func (p *Provider) loadMiddlewares(conf *dynamic.Configuration, namespace, route
 		case gatev1.HTTPRouteFilterRequestHeaderModifier:
 			middlewares[name] = createRequestHeaderModifier(filter.RequestHeaderModifier)
 
+		case gatev1.HTTPRouteFilterResponseHeaderModifier:
+			middlewares[name] = createResponseHeaderModifier(filter.ResponseHeaderModifier)
+
 		case gatev1.HTTPRouteFilterExtensionRef:
 			name, middleware, err := p.loadHTTPRouteFilterExtensionRef(namespace, filter.ExtensionRef)
 			if err != nil {
@@ -599,7 +602,29 @@ func createRequestHeaderModifier(filter *gatev1.HTTPHeaderFilter) *dynamic.Middl
 	}
 
 	return &dynamic.Middleware{
-		RequestHeaderModifier: &dynamic.RequestHeaderModifier{
+		RequestHeaderModifier: &dynamic.HeaderModifier{
+			Set:    sets,
+			Add:    adds,
+			Remove: filter.Remove,
+		},
+	}
+}
+
+// createResponseHeaderModifier does not enforce/check the configuration,
+// as the spec indicates that either the webhook or CEL (since v1.0 GA Release) should enforce that.
+func createResponseHeaderModifier(filter *gatev1.HTTPHeaderFilter) *dynamic.Middleware {
+	sets := map[string]string{}
+	for _, header := range filter.Set {
+		sets[string(header.Name)] = header.Value
+	}
+
+	adds := map[string]string{}
+	for _, header := range filter.Add {
+		adds[string(header.Name)] = header.Value
+	}
+
+	return &dynamic.Middleware{
+		ResponseHeaderModifier: &dynamic.HeaderModifier{
 			Set:    sets,
 			Add:    adds,
 			Remove: filter.Remove,

pkg/provider/kubernetes/gateway/kubernetes_test.go

@@ -1722,7 +1722,77 @@ func TestLoadHTTPRoutes(t *testing.T) {
 					},
 					Middlewares: map[string]*dynamic.Middleware{
 						"default-http-app-1-my-gateway-web-0-364ce6ec04c3d49b19c4-requestheadermodifier-0": {
-							RequestHeaderModifier: &dynamic.RequestHeaderModifier{
+							RequestHeaderModifier: &dynamic.HeaderModifier{
+								Set:    map[string]string{"X-Foo": "Bar"},
+								Add:    map[string]string{"X-Bar": "Foo"},
+								Remove: []string{"X-Baz"},
+							},
+						},
+					},
+					Services: map[string]*dynamic.Service{
+						"default-http-app-1-my-gateway-web-0-wrr": {
+							Weighted: &dynamic.WeightedRoundRobin{
+								Services: []dynamic.WRRService{
+									{
+										Name:   "default-whoami-80",
+										Weight: ptr.To(1),
+									},
+								},
+							},
+						},
+						"default-whoami-80": {
+							LoadBalancer: &dynamic.ServersLoadBalancer{
+								Servers: []dynamic.Server{
+									{
+										URL: "http://10.10.0.1:80",
+									},
+									{
+										URL: "http://10.10.0.2:80",
+									},
+								},
+								PassHostHeader: ptr.To(true),
+								ResponseForwarding: &dynamic.ResponseForwarding{
+									FlushInterval: ptypes.Duration(100 * time.Millisecond),
+								},
+							},
+						},
+					},
+					ServersTransports: map[string]*dynamic.ServersTransport{},
+				},
+				TLS: &dynamic.TLSConfiguration{},
+			},
+		},
+		{
+			desc:  "Simple HTTPRoute, response header modifier",
+			paths: []string{"services.yml", "httproute/filter_response_header_modifier.yml"},
+			entryPoints: map[string]Entrypoint{"web": {
+				Address: ":80",
+			}},
+			expected: &dynamic.Configuration{
+				UDP: &dynamic.UDPConfiguration{
+					Routers:  map[string]*dynamic.UDPRouter{},
+					Services: map[string]*dynamic.UDPService{},
+				},
+				TCP: &dynamic.TCPConfiguration{
+					Routers:           map[string]*dynamic.TCPRouter{},
+					Middlewares:       map[string]*dynamic.TCPMiddleware{},
+					Services:          map[string]*dynamic.TCPService{},
+					ServersTransports: map[string]*dynamic.TCPServersTransport{},
+				},
+				HTTP: &dynamic.HTTPConfiguration{
+					Routers: map[string]*dynamic.Router{
+						"default-http-app-1-my-gateway-web-0-364ce6ec04c3d49b19c4": {
+							EntryPoints: []string{"web"},
+							Service:     "default-http-app-1-my-gateway-web-0-wrr",
+							Rule:        "Host(`example.org`) && PathPrefix(`/`)",
+							Priority:    13,
+							RuleSyntax:  "v3",
+							Middlewares: []string{"default-http-app-1-my-gateway-web-0-364ce6ec04c3d49b19c4-responseheadermodifier-0"},
+						},
+					},
+					Middlewares: map[string]*dynamic.Middleware{
+						"default-http-app-1-my-gateway-web-0-364ce6ec04c3d49b19c4-responseheadermodifier-0": {
+							ResponseHeaderModifier: &dynamic.HeaderModifier{
 								Set:    map[string]string{"X-Foo": "Bar"},
 								Add:    map[string]string{"X-Bar": "Foo"},
 								Remove: []string{"X-Baz"},

pkg/server/middleware/middlewares.go

@@ -397,6 +397,15 @@ func (b *Builder) buildConstructor(ctx context.Context, middlewareName string) (
 		}
 	}
 
+	if config.ResponseHeaderModifier != nil {
+		if middleware != nil {
+			return nil, badConf
+		}
+		middleware = func(next http.Handler) (http.Handler, error) {
+			return headermodifier.NewResponseHeaderModifier(ctx, next, *config.ResponseHeaderModifier, middlewareName), nil
+		}
+	}
+
 	if config.RequestRedirect != nil {
 		if middleware != nil {
 			return nil, badConf