feat: add annotation to allow to add custom response headers (#9742)

* add custom headers

Signed-off-by: Christian Groschupp <christian@groschupp.org>

* add tests

Signed-off-by: Christian Groschupp <christian@groschupp.org>

* add docs

* update copyright

* change comments

* add e2e test customheaders

* add custom headers validation

* remove escapeLiteralDollar filter

* validate value in custom headers

* add regex for header value

* fix annotation test

* Revert "remove escapeLiteralDollar filter"

This reverts commit ab48392b60dee4ce146a4c17e046849f9633c7fb.

* add annotationConfig

* fix test

* fix golangci-lint findings

* fix: add missung exp module

---------

Signed-off-by: Christian Groschupp <christian@groschupp.org>

test/e2e/annotations/customheaders.go

@@ -0,0 +1,110 @@
+/*
+Copyright 2023 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package annotations
+
+import (
+	"fmt"
+	"net/http"
+	"strings"
+
+	"github.com/onsi/ginkgo/v2"
+
+	"k8s.io/ingress-nginx/test/e2e/framework"
+)
+
+const (
+	customHeaderHost = "custom-headers"
+)
+
+var _ = framework.DescribeAnnotation("custom-headers-*", func() {
+	f := framework.NewDefaultFramework("custom-headers")
+
+	ginkgo.BeforeEach(func() {
+		f.NewEchoDeployment()
+	})
+
+	ginkgo.It("should return status code 200 when no custom-headers is configured", func() {
+		ing := framework.NewSingleIngress(customHeaderHost, "/", customHeaderHost, f.Namespace, framework.EchoService, 80, nil)
+		f.EnsureIngress(ing)
+
+		f.WaitForNginxServer(customHeaderHost,
+			func(server string) bool {
+				return strings.Contains(server, "server_name custom-headers")
+			})
+
+		f.HTTPTestClient().
+			GET("/").
+			WithHeader("Host", customHeaderHost).
+			Expect().
+			Status(http.StatusOK).
+			Body().Contains(fmt.Sprintf("host=%v", customHeaderHost))
+	})
+
+	ginkgo.It("should return status code 503 when custom-headers is configured with an invalid secret", func() {
+		annotations := map[string]string{
+			"nginx.ingress.kubernetes.io/custom-headers": f.Namespace + "/custom-headers",
+		}
+
+		ing := framework.NewSingleIngress(customHeaderHost, "/", customHeaderHost, f.Namespace, framework.EchoService, 80, annotations)
+		f.EnsureIngress(ing)
+
+		f.WaitForNginxServer(customHeaderHost,
+			func(server string) bool {
+				return strings.Contains(server, "server_name custom-headers")
+			})
+
+		f.HTTPTestClient().
+			GET("/").
+			WithHeader("Host", customHeaderHost).
+			Expect().
+			Status(http.StatusServiceUnavailable).
+			Body().Contains("503 Service Temporarily Unavailable")
+	})
+
+	ginkgo.It(`should set "more_set_headers 'My-Custom-Header' '42';" when custom-headers are set`, func() {
+		annotations := map[string]string{
+			"nginx.ingress.kubernetes.io/custom-headers": f.Namespace + "/custom-headers",
+		}
+
+		f.CreateConfigMap("custom-headers", map[string]string{
+			"My-Custom-Header":        "42",
+			"My-Custom-Header-Dollar": "$remote_addr",
+		})
+		f.UpdateNginxConfigMapData("global-allowed-response-headers", "My-Custom-Header,My-Custom-Header-Dollar")
+
+		ing := framework.NewSingleIngress(customHeaderHost, "/", customHeaderHost, f.Namespace, framework.EchoService, 80, annotations)
+		f.EnsureIngress(ing)
+
+		f.WaitForNginxServer(customHeaderHost,
+			func(server string) bool {
+				return strings.Contains(server, `more_set_headers "My-Custom-Header: 42";`)
+			})
+
+		f.HTTPTestClient().
+			GET("/").
+			WithHeader("Host", customHeaderHost).
+			Expect().
+			Status(http.StatusOK).
+			Header("My-Custom-Header").Contains("42")
+		f.HTTPTestClient().
+			GET("/").
+			WithHeader("Host", customHeaderHost).
+			Expect().
+			Status(http.StatusOK).
+			Header("My-Custom-Header-Dollar").Contains("$remote_addr")
+	})
+})