re-add experimental::MetadataCredentialsFromPlugin

src/cpp/client/secure_credentials.cc

@@ -464,8 +464,10 @@ class MetadataCredentialsPluginWrapper final : private internal::GrpcLibrary {
 
 }  // namespace
 
+namespace experimental {
 std::shared_ptr<CallCredentials> MetadataCredentialsFromPlugin(
-    std::unique_ptr<MetadataCredentialsPlugin> plugin) {
+    std::unique_ptr<MetadataCredentialsPlugin> plugin,
+    grpc_security_level min_security_level) {
   grpc::internal::GrpcLibrary init;  // To call grpc_init().
   const char* type = plugin->GetType();
   MetadataCredentialsPluginWrapper* wrapper =
@@ -475,7 +477,15 @@ std::shared_ptr<CallCredentials> MetadataCredentialsFromPlugin(
       MetadataCredentialsPluginWrapper::DebugString,
       MetadataCredentialsPluginWrapper::Destroy, wrapper, type};
   return WrapCallCredentials(grpc_metadata_credentials_create_from_plugin(
-      c_plugin, GRPC_PRIVACY_AND_INTEGRITY, nullptr));
+      c_plugin, min_security_level, nullptr));
+}
+
+}  // namespace experimental
+
+std::shared_ptr<CallCredentials> MetadataCredentialsFromPlugin(
+    std::unique_ptr<MetadataCredentialsPlugin> plugin) {
+  return experimental::MetadataCredentialsFromPlugin(
+      std::move(plugin), GRPC_PRIVACY_AND_INTEGRITY);
 }
 
 }  // namespace grpc