All SlideShare API end points will require https
We already supported SSL for all API endpoints, but to increase security for both our community users and developers we are making it mandatory to move to HTTPS endpoint for all the API calls. Any app that connects to SlideShare should make this change as soon as possible. We will disable http API support by the end of this year.
Also, Check out our RSS feeds! They contain a lot of rich data (including slideshow embed codes and thumbnails) that can be useful in creating your mashup.