Can we pass in a custom header in promtail client

We are trying to use grafana agent to send to a remote Loki instance. As part of auth layer we need to pass an api key in a custom header. I see that remote_write config of Prometheus and OpenTelemetry receiver used by grafana agent allow us to specify a custom header. I don’t see such a feature in clients section of Promtail. Is there such a feature in Promtail?