Steam web API
http://steamcommunity.com/dev
Official supported API 
http://api.steampowered.com/ISteamWebAPIUtil/GetSupportedAPIList/v0001/
Not supported, bud worked API
http://pastebin.com/qsX36TMT
Steam browser protocol
https://developer.valvesoftware.com/wiki/Steam_browser_protocol
Other realization on c++
https://code.google.com/p/pidgin-opensteamworks/
https://github.com/jgeboski/bitlbee-steam