Add an additional information in HTTP header from filebeat to ElasticSearch

Hi,
I want to add an additional information in HTTP header (for authentication on server) in http request from filebeat to ElasticSearch. Is it possible ? Please let me know.

Thanks,
RK

Reading the docs it doesn't seem to be possible: https://www.elastic.co/guide/en/beats/filebeat/master/elasticsearch-output.html

Feel free to add a feature request on github