--header is not used with communication to Fleet Server

[blakerouse]

Overview

At the moment during enrollment the --header flag is only used for adding headers with communication with Elasticsearch, it is not used with communication with Fleet Server. The same --header flag should be used for communication with Fleet Server.

Why?

--header is normally used for reverse proxies that have some type of filtering enabled that doesn't allow a request to be proxied to the proper backend unless a specific header is present.

At the moment we support this for Elasticsearch, but not for communication with Fleet Server.

[elasticmachine]

Pinging @elastic/elastic-agent-control-plane (Team:Elastic-Agent-Control-Plane)