1. A networking device positioned intermediate to a client and server on a computer network, the networking device comprising: a user-defined ruleset including HTTP request rules and HTTP response rules; a configuration tool configured to enable a user to configure the HTTP request rules and HTTP response rules of the user-defined ruleset, wherein the configuration tool receives input from the user defining one or more of the HTTP request rules or the HTTP response rules of the user-defined ruleset using a syntax that allows the user to specify a test condition and an action statement for each of the rules; a request processor configured to receive an incoming HTTP request from the client, apply at least one of the HTTP request rules to the incoming HTTP request to detect the test condition specified by the at least one of the HTTP request rules, to thereby produce a modified HTTP request in accordance with the action statement specified by the at least one of the HTTP request rules, and send the modified HTTP request to the server; and a response processor configured to receive an HTTP response to the modified HTTP request from the server, apply at least one of the HTTP response rules to the HTTP response to detect the test condition specified by the at least one of the HTTP response rules, to thereby produce a modified HTTP response in accordance with the action statement specified by the at least one of the HTTP response rules, and send the modified HTTP response to the client.