We still need virtually all of the existing code “somewhere”. These chunks of code might be large enough or at least prominent enough to warrant their own projects if we’re prepared to manage that many projects:
HTTP client supporting code
There are a lot of candidate components that may end up in common between the IdP and SP. Most of them probably will depend on OpenSAML, a few don’t. The full list will evolve based on development so is speculative at best at this stage.