Reverse proxy Kibana 7 with ARR in IIS - kibana

Question

I set up some days ago an ELK 7 stack to monitor some logs in one place. For now it perfectly operational and works well from inside the network. I now want to access Kibana from outside the network without the need of a VPN.
I already have a website running in IIS which is served through a global reverse proxy. The website itself is doing nothing but there are 2 WebApplications under it (there's just a little app at the webiste root doing a redirect to the right app depending of the source of the request).
So at the moment, i have the following URLs available (servername could be either my machine name when i'm on the intranet or the external domain when i'm remoting) :
http(s)://servername/app1
http(s)://servername/app2
Now i would like to be able to get the following URL working to access Kibana
http(s)://servername/elk
For now i didn't manage to make it work - even internally - (so without involving the first global reverse proxy).
I set up a application under a website dedicated for testing purpose (so it won't mess with the real website). This is an extract of my web.config file for this application :
<configuration>
<system.webServer>
<rewrite>
<rules>
<rule name="KibanaProxy">
<match url="(.*)" />
<action type="Rewrite" url="http://kibanahost:5601/{R:1}" />
</rule>
</rules>
<outboundRules>
<rule name="KibanaRedirect" preCondition="Redirect">
<match serverVariable="RESPONSE_Location" pattern="^/(.*)" />
<action type="Rewrite" value="/elk/{R:1}" />
</rule>
<rule name="KibanaContent" preCondition="ResponseIsHtml1">
<match filterByTags="A, Area, Base, Form, Frame, Head, IFrame, Input, Link, Script" pattern="^/(.*)" />
<action type="Rewrite" value="/elk/{R:1}" />
</rule>
</outboundRules>
</rewrite>
</system.webServer>
</configuration>
I wrote a rule to handle the first redirect done when accessing the Kibana root and i tried to add a rewrite rule so external resources can be accessed also. It seems like i have still some other rewrites to do mainly because of URL inside bootstrap.js and such things like CSS... It seems like it's a pain to achieve and i wonder if anyone managed to accomplish such a proxying. If i can proxy Kibana correctly internally, i would be able to add an authentication layer thanks to IIS before trying to expose it over the internet through the global reverse proxy.