Presently HttpCore provides support for HTTP CONNECT method for establishing end-to-end tunnels across HTTP proxies as specified in the RFC 2817. However, HttpCore currently does not support 'Upgrade' / 101 (Switching Protocols) handshaking, which does not seem as widely used by the common HTTP agents and servers as HTTP CONNECT.
Adding support for upgrading plain connections to TLS will require significant amount of work and is likely to call for non-trivial changes to the existing protocol handlers.
We currently have no resources within the project to assign to this task, but will gladly assist an external contributor willing to work on adding support for 'Upgrade' / 101 (Switching Protocols) handshaking to HttpCore. This may also be a good topic for a Google Summer of Code project or a similar program.