First doesn’t work for me, most likely that’s because I have just registered and some deprecated features are not available for me, but https://api.twitch.tv/kraken/ works fine, thanks a lot.
I have already found chrome extension to do that: https://chrome.google.com/webstore/detail/twitch-username-and-user/laonpoebfalkjijglbjbnkfndibbcoon/related