set the webentry point, s_webentryhost, to the hostname justanexample
set the webentry domain, s_webentrydomain, to the domain name like example.com
set the active webport, s_active_webport, to the port where the reverse proxy server listen for client requests. For example port 80 for HTTP or 443 for HTTPS.
set the webentry protocol, s_webentryurlprotocol, to the protocol value the clients use to access the reverse proxy server.
set the login page, s_login_page, to webentryprotocol://webentrypoint.webentrydomain:active webport. Replace
set the external url, s_external_url to the full url like https://justanexample.example.com
After running autoconfig, the problem was solved and it was no longer directing to internal app tiers.
Peculiar thing was that, they were using numeric IP to reach the extranet web tier. I advsied them to find out from the client what name was reserved for the site and use that instead. It turned out that the name was being used for an existing web shop and iStore was supposed to replace it. I told them that they could use a free DNS provider and get a name for their IP in just a few seconds which would give them a proper URL to test instead of using a numeric IP. Furthermore, numeric IP is not supported as the URL by Oracle Apps. So I reserved a name for them through a free DNS service www.dns2go.com. I had used their services long back for a similar purpose.
In case you have a similar problem, you could also use a free DNS service like www.dns2go.com to get a name for your global IP. It would be name_given_by_you.dns2go.com