Apache Reverse Proxy for Kibana 5

it's just impossible to simply configure Kibana 5 behind an Apache Reverse Proxy

Impossible? Right...

There is no official documentation

all the "working" solutions on Google

450 results found: reverse proxy site:elastic.co - Google Search
have you tried them all?

Did someone already succeed to configure an Apache Reverse Proxy (Apache 2.4.10) for Kibana 5 ?

yes. with this guide: