I have a misbehaving origin that when it has an error page it is not setting a content-type header. This is then a problem as we're sitting behind Edgecast and they default to application/octet-stream which causes browsers to try and download the file. Is there any way I can get apache to set a content type response header if there isn't one?
There is the Default-Type config option: http://httpd.apache.org/docs/current/mod/core.html#defaulttype
Not sure if you can use it depending on your failure scenario, but it's probably worth looking at along with custom error documents: http://httpd.apache.org/docs/trunk/mod/core.html#errordocument
There's a bit at the bottom of that to sue it with mod_proxy