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>

internal/ingress/annotations/customheaders/main_test.go

@@ -0,0 +1,113 @@
+/*
+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 customheaders
+
+import (
+	"reflect"
+	"testing"
+
+	api "k8s.io/api/core/v1"
+	networking "k8s.io/api/networking/v1"
+	meta_v1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/ingress-nginx/internal/ingress/annotations/parser"
+	"k8s.io/ingress-nginx/internal/ingress/defaults"
+	"k8s.io/ingress-nginx/internal/ingress/resolver"
+)
+
+func buildIngress() *networking.Ingress {
+	return &networking.Ingress{
+		ObjectMeta: meta_v1.ObjectMeta{
+			Name:      "foo",
+			Namespace: api.NamespaceDefault,
+		},
+		Spec: networking.IngressSpec{
+			DefaultBackend: &networking.IngressBackend{
+				Service: &networking.IngressServiceBackend{
+					Name: "default-backend",
+					Port: networking.ServiceBackendPort{
+						Number: 80,
+					},
+				},
+			},
+		},
+	}
+}
+
+type mockBackend struct {
+	resolver.Mock
+}
+
+// GetDefaultBackend returns the backend that must be used as default
+func (m mockBackend) GetDefaultBackend() defaults.Backend {
+	return defaults.Backend{
+		AllowedResponseHeaders: []string{"Content-Type", "Access-Control-Max-Age"},
+	}
+}
+
+func TestCustomHeadersParseInvalidAnnotations(t *testing.T) {
+	ing := buildIngress()
+	configMapResolver := mockBackend{}
+	configMapResolver.ConfigMaps = map[string]*api.ConfigMap{}
+
+	_, err := NewParser(configMapResolver).Parse(ing)
+	if err != nil {
+		t.Errorf("expected error parsing ingress with custom-response-headers")
+	}
+
+	data := map[string]string{}
+	data[parser.GetAnnotationWithPrefix("custom-headers")] = "custom-headers-configmap"
+	ing.SetAnnotations(data)
+	i, err := NewParser(&resolver.Mock{}).Parse(ing)
+	if err == nil {
+		t.Errorf("expected error parsing ingress with custom-response-headers")
+	}
+	if i != nil {
+		t.Errorf("expected %v but got %v", nil, i)
+	}
+}
+
+func TestCustomHeadersParseAnnotations(t *testing.T) {
+	ing := buildIngress()
+
+	data := map[string]string{}
+	data[parser.GetAnnotationWithPrefix("custom-headers")] = "custom-headers-configmap"
+	ing.SetAnnotations(data)
+
+	configMapResolver := mockBackend{}
+	configMapResolver.ConfigMaps = map[string]*api.ConfigMap{}
+
+	configMapResolver.ConfigMaps["custom-headers-configmap"] = &api.ConfigMap{Data: map[string]string{"Content-Type": "application/json", "Access-Control-Max-Age": "600"}}
+
+	i, err := NewParser(configMapResolver).Parse(ing)
+	if err != nil {
+		t.Errorf("unexpected error parsing ingress with custom-response-headers: %s", err)
+	}
+	val, ok := i.(*Config)
+	if !ok {
+		t.Errorf("expected a *Config type")
+	}
+
+	expectedResponseHeaders := map[string]string{}
+	expectedResponseHeaders["Content-Type"] = "application/json"
+	expectedResponseHeaders["Access-Control-Max-Age"] = "600"
+
+	c := &Config{expectedResponseHeaders}
+
+	if !reflect.DeepEqual(c, val) {
+		t.Errorf("expected %v but got %v", c, val)
+	}
+}