feat(admission) implement validation for secret-based credentials

The validation currently consists of verifying if each and every
required field is provided by the user or not.

In future, the validation can be made smarter to include an Admin API
call to Kong to verify if the creation of such a credential will succeed
or not (see TODO in code).

From #446

internal/admission/server.go

@@ -9,6 +9,7 @@ import (
 	configuration "github.com/kong/kubernetes-ingress-controller/internal/apis/configuration/v1"
 	"github.com/pkg/errors"
 	admission "k8s.io/api/admission/v1beta1"
+	corev1 "k8s.io/api/core/v1"
 	meta "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/runtime/serializer"
@@ -78,6 +79,10 @@ var (
 		Group:    configuration.SchemeGroupVersion.Group,
 		Version:  configuration.SchemeGroupVersion.Version,
 		Resource: "kongplugins"}
+	secretGVResource = meta.GroupVersionResource{
+		Group:    corev1.SchemeGroupVersion.Group,
+		Version:  corev1.SchemeGroupVersion.Version,
+		Resource: "secrets"}
 )
 
 func (a Server) handleValidation(request admission.AdmissionRequest) (
@@ -115,6 +120,24 @@ func (a Server) handleValidation(request admission.AdmissionRequest) (
 		if err != nil {
 			return nil, err
 		}
+	case secretGVResource:
+		secret := corev1.Secret{}
+		deserializer := codecs.UniversalDeserializer()
+		_, _, err = deserializer.Decode(request.Object.Raw,
+			nil, &secret)
+		if err != nil {
+			return nil, err
+		}
+		if _, ok = secret.Data["credType"]; !ok {
+			// secret does not look like a credential resource in Kong
+			ok = true
+			break
+		}
+
+		ok, message, err = a.Validator.ValidateCredential(secret)
+		if err != nil {
+			return nil, err
+		}
 	default:
 		return nil, errors.Errorf("unknown resource type to validate: %s/%s %s",
 			request.Resource.Group, request.Resource.Version,

internal/admission/server_test.go

@@ -10,6 +10,7 @@ import (
 	"github.com/pkg/errors"
 	"github.com/stretchr/testify/assert"
 	admission "k8s.io/api/admission/v1beta1"
+	corev1 "k8s.io/api/core/v1"
 )
 
 var decoder = codecs.UniversalDeserializer()
@@ -30,6 +31,11 @@ func (v KongFakeValidator) ValidatePlugin(
 	return v.Result, v.Message, v.Error
 }
 
+func (v KongFakeValidator) ValidateCredential(
+	secret corev1.Secret) (bool, string, error) {
+	return v.Result, v.Message, v.Error
+}
+
 func TestServeHTTPBasic(t *testing.T) {
 	assert := assert.New(t)
 	res := httptest.NewRecorder()

internal/admission/validator.go

@@ -1,16 +1,20 @@
 package admission
 
 import (
+	"strings"
+
 	"github.com/golang/glog"
 	"github.com/hbagdi/go-kong/kong"
 	configuration "github.com/kong/kubernetes-ingress-controller/internal/apis/configuration/v1"
 	"github.com/pkg/errors"
+	corev1 "k8s.io/api/core/v1"
 )
 
 // KongValidator validates Kong entities.
 type KongValidator interface {
 	ValidateConsumer(consumer configuration.KongConsumer) (bool, string, error)
 	ValidatePlugin(consumer configuration.KongPlugin) (bool, string, error)
+	ValidateCredential(secret corev1.Secret) (bool, string, error)
 }
 
 // KongHTTPValidator implements KongValidator interface to validate Kong
@@ -83,6 +87,58 @@ func (validator KongHTTPValidator) ValidatePlugin(
 	return true, "", nil
 }
 
+var (
+	// TODO dynamically fetch these from Kong
+	credTypeToFields = map[string][]string{
+		"key-auth":   {"key"},
+		"basic-auth": {"username", "password"},
+		"hmac-auth":  {"username", "secret"},
+		"oauth2":     {"name", "client_id", "client_secret", "redirect_uris"},
+		"jwt":        {"algorithm", "rsa_public_key", "key", "secret"},
+		"acl":        {"group"},
+	}
+)
+
+// ValidateCredential checks if the secret contains a credential meant to
+// be installed in Kong. If so, then it verifies if all the required fields
+// are present in it or not. If valid, it returns true with an empty string,
+// else it returns false with the error messsage. If an error happens during
+// validation, error is returned.
+func (validator KongHTTPValidator) ValidateCredential(
+	secret corev1.Secret) (bool, string, error) {
+
+	credTypeBytes, ok := secret.Data["credType"]
+	if !ok {
+		// doesn't look like a credential resource
+		return true, "", nil
+	}
+	credType := string(credTypeBytes)
+
+	fields, ok := credTypeToFields[credType]
+	if !ok {
+		return false, "invalid credential type: " + credType, nil
+	}
+
+	var missingFields []string
+	for _, field := range fields {
+		if _, ok := secret.Data[field]; !ok {
+			missingFields = append(missingFields, field)
+		}
+	}
+	if len(missingFields) != 0 {
+		return false, "missing required field(s): " +
+			strings.Join(missingFields, ", "), nil
+	}
+
+	// TODO add unique key violation detection
+	// For each credential, there is a unique column, like key for key-auth,
+	// username for basic-auth; make an API call to Kong's Admin API
+	// and verify if there will be a violation, similar to how it's done
+	// for KongConsumer; return error if the resource is already present in
+	// Kong.
+	return true, "", nil
+}
+
 func empty(s *string) bool {
 	return s == nil && *s == ""
 }

internal/admission/validator_test.go

@@ -0,0 +1,91 @@
+package admission
+
+import (
+	"testing"
+
+	corev1 "k8s.io/api/core/v1"
+)
+
+func TestKongHTTPValidator_ValidateCredential(t *testing.T) {
+	type args struct {
+		secret corev1.Secret
+	}
+	tests := []struct {
+		name        string
+		args        args
+		wantOK      bool
+		wantMessage string
+		wantErr     bool
+	}{
+		{
+			name: "valid key-auth credential",
+			args: args{
+				secret: corev1.Secret{
+					Data: map[string][]byte{
+						"key":      []byte("foo"),
+						"credType": []byte("key-auth"),
+					},
+				},
+			},
+			wantOK:      true,
+			wantMessage: "",
+			wantErr:     false,
+		},
+		{
+			name: "invalid key-auth credential",
+			args: args{
+				secret: corev1.Secret{
+					Data: map[string][]byte{
+						"key-wrong": []byte("foo"),
+						"credType":  []byte("key-auth"),
+					},
+				},
+			},
+			wantOK:      false,
+			wantMessage: "missing required field(s): key",
+			wantErr:     false,
+		},
+		{
+			name: "invalid credential type",
+			args: args{
+				secret: corev1.Secret{
+					Data: map[string][]byte{
+						"credType": []byte("foo"),
+					},
+				},
+			},
+			wantOK:      false,
+			wantMessage: "invalid credential type: foo",
+			wantErr:     false,
+		},
+		{
+			name: "non-kong secrets are passed",
+			args: args{
+				secret: corev1.Secret{
+					Data: map[string][]byte{
+						"key": []byte("foo"),
+					},
+				},
+			},
+			wantOK:      true,
+			wantMessage: "",
+			wantErr:     false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			validator := KongHTTPValidator{}
+			got, got1, err := validator.ValidateCredential(tt.args.secret)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("KongHTTPValidator.ValidateCredential() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if got != tt.wantOK {
+				t.Errorf("KongHTTPValidator.ValidateCredential() got = %v, want %v", got, tt.wantOK)
+			}
+			if got1 != tt.wantMessage {
+				t.Errorf("KongHTTPValidator.ValidateCredential() got1 = %v, want %v", got1, tt.wantMessage)
+			}
+		})
+	}
+}