Actually more of a discussion than an answer, but it might be interesting to a few others.
I work as a super user for Confluence in tech company. I have gotten questions about how to include HTML content to a Confluence page, since we now use it for project documentation.
There is a macro for that, I know, but then it isn't HTML only: It is a set of HTML files, with navigation links, and JavaScript, and autogenerated images. Doxygen output is one example of the things I'm talking about.
My answer so far is: Don't bother, use a normal web server. And my thought is: Isn't this like asking for a browser plugin to run inside their browser?
Is there anyone who has a better answer?