feat: TLS support for External Data Providers

constraint/config/crds/externaldata.gatekeeper.sh_providers.yaml

@@ -35,6 +35,15 @@ spec:
           spec:
             description: Spec defines the Provider specifications.
             properties:
+              caBundle:
+                description: CABundle is a base64-encoded string that contains the
+                  TLS CA bundle in PEM format. It is used to verify the signature
+                  of the provider's certificate.
+                type: string
+              insecureTLSSkipVerify:
+                description: InsecureTLSSkipVerify skips the verification of Provider's
+                  certificate if enabled.
+                type: boolean
               timeout:
                 description: Timeout is the timeout when querying the provider.
                 type: integer

constraint/deploy/crds.yaml

@@ -366,6 +366,15 @@ spec:
           spec:
             description: Spec defines the Provider specifications.
             properties:
+              caBundle:
+                description: CABundle is a base64-encoded string that contains the
+                  TLS CA bundle in PEM format. It is used to verify the signature
+                  of the provider's certificate.
+                type: string
+              insecureTLSSkipVerify:
+                description: InsecureTLSSkipVerify skips the verification of Provider's
+                  certificate if enabled.
+                type: boolean
               timeout:
                 description: Timeout is the timeout when querying the provider.
                 type: integer

constraint/go.mod

@@ -42,6 +42,7 @@ require (
 	github.com/emicklei/go-restful v2.9.5+incompatible // indirect
 	github.com/evanphx/json-patch v4.12.0+incompatible // indirect
 	github.com/felixge/httpsnoop v1.0.2 // indirect
+	github.com/fsnotify/fsnotify v1.5.4 // indirect
 	github.com/ghodss/yaml v1.0.0 // indirect
 	github.com/go-logr/logr v1.2.3 // indirect
 	github.com/go-openapi/jsonpointer v0.19.5 // indirect

constraint/pkg/apis/externaldata/v1alpha1/provider_types.go

@@ -25,6 +25,11 @@ type ProviderSpec struct {
 	URL string `json:"url,omitempty"`
 	// Timeout is the timeout when querying the provider.
 	Timeout int `json:"timeout,omitempty"`
+	// CABundle is a base64-encoded string that contains the TLS CA bundle in PEM format.
+	// It is used to verify the signature of the provider's certificate.
+	CABundle string `json:"caBundle,omitempty"`
+	// InsecureTLSSkipVerify skips the verification of Provider's certificate if enabled.
+	InsecureTLSSkipVerify bool `json:"insecureTLSSkipVerify,omitempty"`
 }
 
 // +genclient

constraint/pkg/client/drivers/local/args.go

@@ -9,6 +9,7 @@ import (
 	"github.com/open-policy-agent/opa/storage"
 	"github.com/open-policy-agent/opa/topdown/print"
 	opatypes "github.com/open-policy-agent/opa/types"
+	"sigs.k8s.io/controller-runtime/pkg/certwatcher"
 )
 
 type Arg func(*Driver) error
@@ -115,6 +116,22 @@ func DisableBuiltins(builtins ...string) Arg {
 	}
 }
 
+func AddExternalDataClientCertWatcher(clientCertWatcher *certwatcher.CertWatcher) Arg {
+	return func(d *Driver) error {
+		d.clientCertWatcher = clientCertWatcher
+
+		return nil
+	}
+}
+
+func EnableExternalDataClientAuth() Arg {
+	return func(d *Driver) error {
+		d.enableExternalDataClientAuth = true
+
+		return nil
+	}
+}
+
 // Externs sets the fields under `data` that Rego in ConstraintTemplates
 // can access. If unset, all fields can be accessed. Only fields recognized by
 // the system can be enabled.

constraint/pkg/client/drivers/local/builtin.go

@@ -20,7 +20,12 @@ func externalDataBuiltin(d *Driver) func(bctx rego.BuiltinContext, regorequest *
 			return externaldata.HandleError(http.StatusBadRequest, err)
 		}
 
-		externaldataResponse, statusCode, err := d.sendRequestToProvider(bctx.Context, &provider, regoReq.Keys)
+		clientCert, err := d.getTLSCertificate()
+		if err != nil {
+			return externaldata.HandleError(http.StatusBadRequest, err)
+		}
+
+		externaldataResponse, statusCode, err := d.sendRequestToProvider(bctx.Context, &provider, regoReq.Keys, clientCert)
 		if err != nil {
 			return externaldata.HandleError(statusCode, err)
 		}

constraint/pkg/client/drivers/local/driver.go

@@ -3,6 +3,7 @@ package local
 import (
 	"bytes"
 	"context"
+	"crypto/tls"
 	"encoding/json"
 	"fmt"
 	"sort"
@@ -22,6 +23,7 @@ import (
 	"github.com/open-policy-agent/opa/topdown/print"
 	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
 	"k8s.io/utils/pointer"
+	"sigs.k8s.io/controller-runtime/pkg/certwatcher"
 )
 
 const (
@@ -61,6 +63,13 @@ type Driver struct {
 
 	// sendRequestToProvider allows Rego to send requests to the provider specified in external_data.
 	sendRequestToProvider externaldata.SendRequestToProvider
+
+	// enableExternalDataClientAuth enables the injection of a TLS certificate into an HTTP client
+	// that is used to communicate with providers.
+	enableExternalDataClientAuth bool
+
+	// clientCertWatcher is a watcher for the TLS certificate used to communicate with providers.
+	clientCertWatcher *certwatcher.CertWatcher
 }
 
 // AddTemplate adds templ to Driver. Normalizes modules into usable forms for
@@ -321,6 +330,18 @@ func (d *Driver) Dump(ctx context.Context) (string, error) {
 	return string(b), nil
 }
 
+func (d *Driver) getTLSCertificate() (*tls.Certificate, error) {
+	if !d.enableExternalDataClientAuth {
+		return nil, nil
+	}
+
+	if d.clientCertWatcher == nil {
+		return nil, fmt.Errorf("certWatcher should not be nil when enableExternalDataClientAuth is true")
+	}
+
+	return d.clientCertWatcher.GetCertificate(nil)
+}
+
 // rewriteModulePackage rewrites the module's package path to path.
 func rewriteModulePackage(module *ast.Module) error {
 	pathParts := ast.Ref([]*ast.Term{ast.VarTerm(templatePath)})