Allow forwarding of proxy/request headers to ES

[psk-ixolit]

This is an implementation for #349 and #295.

It extends the host configuration with a forward_headers field.
It specifies which headers of the original request towards cerebro should be forwarded to the ES instance.

[moliware]

Hi! Thanks for the contribution. I'll have a deeper look before merging it.

[moliware]

Hi @psk-ixolit, I remamed the property to headers-whitelist so that it's similar to kibana's naming (they have a similar setting called: elasticsearch.requestHeadersWhitelist).

Thank you very much for contributing, I'll ty to release a new version by the end of this week. As I don't use search guard, would be much appreciated if you could test it and give us feedback. Thanks!

[arturmartins]

@moliware: any chance to get a new release/version soon?

[kiblik]

This parameter looks pretty nice but it doesn't work for me.

I tried to set the same headers which work for kibana (requestHeadersWhitelist) but ES returns HTTP 401.

When I tried to inspect traffic (tcpdump 'tcp port 9200 or tcp port 9000') I saw that Cerebro doesn't pass my headers to requests.