Write transparent HTTP Proxy script in PHP

Is there an easy forwarding/transparent php proxy script that I can host on my web server? These are my conditions:

1. I'm using free web hosting, so I have pretty much no control over my machine. Otherwise I could use Perl's HTTP::Proxy module. This means no root password. It does run php though.

2. I already have a server running on port 80. What I mean is I would like to put a php script as index.php on my server that will forward all requests.

3. I don't want a script like PHProxy or Glype where I go to the site, then enter a URL. I want a server so I can enter proxy.example.com:80 in Firefox's or IE's or whatever's proxy settings and it will forward all requests to the server.

4. Preferably (though not fatal if not possible) I would like for it to pass on the USER_AGENT environmental variable (That's the browser) instead of setting itself to be the USER_AGENT

5. I can't start a new Daemon. My开发者_如何学C server won't allow it.

Is there a script that will do this? If so, which?

No, I'm fairly sure this is not possible on shared hosting. It will fail your condition number 3. This needs support on web server level (e.g. using Apache's mod_proxy)

For this to work, you would have to set up the remote server to be able to deal with proxied requests. No sane web server will offer that possibility.