Is there any best practice method (and preferably documented) way of revealing the True IP of a user using a HTTP(S) connection?
I.e.: To be able to uncover the true IP from transparent as well as anonymous proxies wherever possible.
If the connection uses proxies which are correctly implemented, discovering the ip through http or tcp can be difficult. You may have some luck in getting closer to the ip using DNS instead. for If you generate the page dynamically to contain an image located at a domain that you control, e.g.
the browser will perform a lookup on 123123.deanonymize.mydomain.com. This will result in a recursive DNS-query that eventually will reach your dns for mydomain.com. The query will originate from whatever dns the victim is using, typically the ISP. So, while it will not give you the exact IP, it may point you in a general direction.
AFAIK, this method works even if the victim uses TOR in vanilla mode, see https://trac.torproject.org/projects/tor/wiki/doc/PreventingDnsLeaksInTor for more information.
Another way may be to use a java-applet to figure out the IP at the client side, but I'm not up-to-date on what limits are in place for that nowadays.