From ba308fa2a3335199682811a7f0f8daed352a4878 Mon Sep 17 00:00:00 2001
From: Ali Aqel <aliaqel@stripe.com>
Date: Wed, 31 Jan 2024 17:47:41 +0000
Subject: [PATCH] Add flag to override GRPC Authority Header

---
 CHANGELOG.md                 |  1 +
 cmd/adapter/main.go          | 18 ++++++++++--------
 pkg/metricsservice/client.go |  7 ++++++-
 3 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 73b4a04231b..85ee889d599 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -62,6 +62,7 @@ Here is an overview of all new **experimental** features:
 
 ### Improvements
 
+- **General**: Add command-line flag in Adapter to allow override of GRPC Authority Header ([#5449](https://github.com/kedacore/keda/issues/5449))
 - **General**: Add OPENTELEMETRY flag in e2e test YAML ([#5375](https://github.com/kedacore/keda/issues/5375))
 
 ### Fixes
diff --git a/cmd/adapter/main.go b/cmd/adapter/main.go
index c63a973c7f2..73844494fb5 100644
--- a/cmd/adapter/main.go
+++ b/cmd/adapter/main.go
@@ -56,12 +56,13 @@ type Adapter struct {
 var logger = klogr.New().WithName("keda_metrics_adapter")
 
 var (
-	adapterClientRequestQPS   float32
-	adapterClientRequestBurst int
-	metricsAPIServerPort      int
-	disableCompression        bool
-	metricsServiceAddr        string
-	profilingAddr             string
+	adapterClientRequestQPS      float32
+	adapterClientRequestBurst    int
+	metricsAPIServerPort         int
+	disableCompression           bool
+	metricsServiceAddr           string
+	profilingAddr                string
+	metricssServiceGRPCAuthority string
 )
 
 func (a *Adapter) makeProvider(ctx context.Context) (provider.ExternalMetricsProvider, <-chan struct{}, error) {
@@ -123,7 +124,7 @@ func (a *Adapter) makeProvider(ctx context.Context) (provider.ExternalMetricsPro
 	}
 
 	logger.Info("Connecting Metrics Service gRPC client to the server", "address", metricsServiceAddr)
-	grpcClient, err := metricsservice.NewGrpcClient(metricsServiceAddr, a.SecureServing.ServerCert.CertDirectory)
+	grpcClient, err := metricsservice.NewGrpcClient(metricsServiceAddr, a.SecureServing.ServerCert.CertDirectory, metricssServiceGRPCAuthority)
 	if err != nil {
 		logger.Error(err, "error connecting Metrics Service gRPC client to the server", "address", metricsServiceAddr)
 		return nil, nil, err
@@ -232,7 +233,8 @@ func main() {
 	cmd.Flags().StringVar(&cmd.Message, "msg", "starting adapter...", "startup message")
 	cmd.Flags().AddGoFlagSet(flag.CommandLine) // make sure we get the klog flags
 	cmd.Flags().IntVar(&metricsAPIServerPort, "port", 8080, "Set the port for the metrics API server")
-	cmd.Flags().StringVar(&metricsServiceAddr, "metrics-service-address", generateDefaultMetricsServiceAddr(), "The address of the gRPRC Metrics Service Server.")
+	cmd.Flags().StringVar(&metricsServiceAddr, "metrics-service-address", generateDefaultMetricsServiceAddr(), "The address of the GRPC Metrics Service Server.")
+	cmd.Flags().StringVar(&metricssServiceGRPCAuthority, "metrics-service-grpc-authority", "", "Host Authority override for the Metrics Service if the Host Authority is not the same as the address used for the GRPC Metrics Service Server.")
 	cmd.Flags().StringVar(&profilingAddr, "profiling-bind-address", "", "The address the profiling would be exposed on.")
 	cmd.Flags().Float32Var(&adapterClientRequestQPS, "kube-api-qps", 20.0, "Set the QPS rate for throttling requests sent to the apiserver")
 	cmd.Flags().IntVar(&adapterClientRequestBurst, "kube-api-burst", 30, "Set the burst for throttling requests sent to the apiserver")
diff --git a/pkg/metricsservice/client.go b/pkg/metricsservice/client.go
index 28b7b49f204..401398b4439 100644
--- a/pkg/metricsservice/client.go
+++ b/pkg/metricsservice/client.go
@@ -36,7 +36,7 @@ type GrpcClient struct {
 	connection *grpc.ClientConn
 }
 
-func NewGrpcClient(url, certDir string) (*GrpcClient, error) {
+func NewGrpcClient(url, certDir, authority string) (*GrpcClient, error) {
 	defaultConfig := `{
 		"methodConfig": [{
 		  "timeout": "3s",
@@ -57,6 +57,11 @@ func NewGrpcClient(url, certDir string) (*GrpcClient, error) {
 		grpc.WithTransportCredentials(creds),
 		grpc.WithDefaultServiceConfig(defaultConfig),
 	}
+
+	if authority != "" {
+		opts = append(opts, grpc.WithAuthority(authority))
+	}
+
 	conn, err := grpc.Dial(url, opts...)
 	if err != nil {
 		return nil, err