I realize there is already a question similar to this one, but this is somewhat of a follow-up.
I understand that a reverse proxy server by itself is hardly useful as a web app security measure because it just kind of "hides" the server behind it, protecting it from fingerprinting, DDoS possibly, yada yada. However, I believe that implementing say snort + squid might accomplish some application-level security because you could analyze traffic for common attack patterns. But I have not seen very much info on the net about what products, open source projects, or even just recipes for this type of system are available.
The motivation for this question is that I support an OLD legacy app that is based on a heavily modded, insecure, and un-upgradable version of Apache2. I CANNOT just place mod_security2 in the conf, it will not work (I can't get the sources to this messed up old distribution of apache to compile mod_security2). So, I thought the next best thing would be to implement a reverse proxy type of solution, since then not only could this solve my immediate problem for this legacy app, but also if set up correctly I could see it being used for future apps as well - central web app security.
Is my mode of thinking incorrect? If it is not totally off-base, there must be some existing solutions, products, projects, recipes, etc out there. Is squid+snort all I need?
EDIT: And how does this all work when I need to do this with encrypted traffic as well?