An SSL intercepting proxy like Squid will do what you're looking for, insofar as the HTTP(S) protocol. Doing that at a gateway level, instead of on the client i

An SSL intercepting proxy like Squid will do what you're looking for, insofar as the HTTP(S) protocol. Doing that at a gateway level, instead of on the client itself, loses visibility into process IDs or other client-local state. The old Microsoft Proxy (and later their ISA Server product) used a proprietary encapsulation between the client and the proxy server that exposed client-local state to the proxy server to let you do "magical" stuff like filtering by process name or username at a gateway level. I wish there was a free software solution that did that.