diff --git a/grpc.go b/grpc.go
index e1043af..c090065 100644
--- a/grpc.go
+++ b/grpc.go
@@ -123,7 +123,7 @@ func (g *grpcClient) call(ctx context.Context, node *registry.Node, req client.R
 	if md, ok := metadata.FromContext(ctx); ok {
 		header = make(map[string]string, len(md))
 		for k, v := range md {
-			header[k] = v
+			header[strings.ToLower(k)] = v
 		}
 	} else {
 		header = make(map[string]string)
@@ -133,9 +133,12 @@ func (g *grpcClient) call(ctx context.Context, node *registry.Node, req client.R
 	header["timeout"] = fmt.Sprintf("%d", opts.RequestTimeout)
 	// set the content type for the request
 	header["x-content-type"] = req.ContentType()
+
 	// set the authorization token if one is saved locally
-	if token, err := config.Get("token"); err == nil && len(token) > 0 {
-		header["authorization"] = BearerScheme + token
+	if len(header["authorization"]) == 0 {
+		if token, err := config.Get("token"); err == nil && len(token) > 0 {
+			header["authorization"] = BearerScheme + token
+		}
 	}
 
 	md := gmetadata.New(header)