Check on GitHub.com. It is a free site and there is a lot of good reverse engineered API data with explicit instructions. (I control my plug from SmartThings using information from GitHub.

Right, Tplink doesn't provide the API officially, but you can try to have a search and find something some info about API of all vendors on Github.

Actually, I have already integrated the plugs and bulbs with SmartThings. Do all basic control plus read the energy meter data. The API is fairly will documented on GitHub.

Some items:
1. Comms are TCP or UDP, not HTTP. Can use HTTP with cloud.
2. Messages are "encrypted"; however, that is solved in the documentation.