IIS8 Sharepoint Site Reverse Proxy - Error 502

Hi,

I'm trying to configure a rule such as the one that follows for a SP site, but I'm getting error 502.

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <system.webServer>
        <rewrite>
            <rules>
  <rule name="CFNUKReverseProxy" enabled="true" stopProcessing="true">
                    <match url="(.*)" />
                    <action type="Rewrite" url="http://contoso-us:46983/{R:1}" logRewrittenUrl="true" />

   <serverVariables>
   <set name="HTTP_ACCEPT_ENCODING" value="" />
   </serverVariables>

                    <conditions>
                  <add input="{HTTPS}" pattern="^ON$" />
                  <add input="{HTTP_HOST}" pattern="^cntus" />
                    </conditions>
                </rule>
               <rule name="CFNUKHttpHttpsRedirect" enabled="true" stopProcessing="true">
                    <match url="(.*)" />
                    <action type="Redirect" url="https://cntus.contoso.com/{R:1}" logRewrittenUrl="true" />
                    <conditions>
   <add input="{HTTPS}" pattern="^OFF$" />
                        <add input="{HTTP_HOST}" matchType="Pattern" pattern="^cntus" ignoreCase="true" negate="false" />
                    </conditions>
                </rule>
            </rules>
        </rewrite>
        <directoryBrowse enabled="false" />
    </system.webServer>
</configuration>

In the SP server I have the following bindings:

http://cntus.contoso.com - :80

https://cntus.contoso.com - :443

And the following AAMs:

http://contoso-us (Default)

https://cntus.contoso.com (Internet)

http://cntus.contoso.com (Internet)

Also, in the server that I'm using for reverse proxy I have the following binding for this site:

http://contoso-cnt:46983

Any ideas?

Thanks in advance!