OK. So I have a CMS written in Java that satisfies the needs of several hundred clients. But periodically, a client will need a specialized application: for example, a class registration database application.
So let's say that I don't feel like writing it or I'm too busy. So I outsource it to someone else but I don't want his/her code on my server because he/she codes in a language not supported by my server environment. So I have the developer host it on a cheap server somewhere else. But I still want the application to appear on my client's main website (hosted by my CMS) within the CMS's template on the client's primary domain.
How can I achieve this? Can I use some type of screen-scraper/proxy that intercepts client requests on my site, passes them to the external server that renders HTML and I then integrate his/her HTML back into my template? How would I deal with subsequent requests back and forth in a truly interactive application?
So that's what I want to do (I think). Does anyone have any insight or experience with this type of thing? What are the pitfalls? Are there products that do this easily?