Custom Proxy Setup

I'm looking for a proxy solution that is able to handle cookies on behalf of a client machine. It can either be a modification of an existing script such as Glype or Squid Cache, or custom coded. Requirements: Must be capable of being installed on an Ubuntu VPS or running under LAMP. If it is a PHP/CGI type proxy it must preserve URL structure: [login to view URL] Must have abaility to find / replace within HTML before parsing to the client: e.g Replace: [foo] with [bar] e.g Replace: [rel="nofollow"] with [] Must have the ability to set custom user agents. All site cookies must be stored / handled server-side. No cookies should be sent to or requested from the client. The script only needs to support one user (which may be connecting from different IPs, web browsers etc). Testing: I should be able to connect through the proxy on one PC (with client cookies disabled), and login to a website (the proxy handles the cookies). Then I should be able to connect through the proxy from another PC/IP and navigate to the same website without having to login again.