HTTP output Plugin

One of my pipelines has a very simple format of a HTTP input plugin where the data is sent straight to a HTTP output plugin.

input { pipeline { address => "pipeline-name" } }

output {
    http {
         url => "address"
	 http_method => "post"
	 headers => ["key", "%{[headers][key]}"]

}
	  stdout { codec => rubydebug 
}

The one problem is that it is removing the headers info from the original HTTP input. I can manually add them like in the above for the key. Different data sets are sent through this all with different headers and I would like to keep on these headers when sending through the output. Is there an option to keep all of the headers from the input data?

Thanks

I guess this isn't an option. I was trying to think of ways to maybe write some Ruby code to dynamically add them in a filter within this pipeline. I am struggling to see how I could then dynamically add them in the headers part of the output.