Make a request to: https://api.twitch.tv/kraken
With your Key in the headers, It’ll return something like (for v3)
Array
(
[identified] => 1
[token] => Array
(
[valid] => 1
[authorization] => Array
(
[scopes] => Array
(
[0] => SCOPE,
[1] => SCOPE
)
[created_at] => 2015-09-05T12:50:07Z
[updated_at] => 2015-09-05T12:50:07Z
)
[user_name] => barrycarlyon
[client_id] => [CLIENTID]
)
[_links] => Array
(
[channel] => https://api.twitch.tv/kraken/channel
[chat] => https://api.twitch.tv/kraken/chat/barrycarlyon
[teams] => https://api.twitch.tv/kraken/teams
[user] => https://api.twitch.tv/kraken/user
[users] => https://api.twitch.tv/kraken/users/barrycarlyon
[streams] => https://api.twitch.tv/kraken/streams/barrycarlyon
[ingests] => https://api.twitch.tv/kraken/ingests
[channels] => https://api.twitch.tv/kraken/channels/barrycarlyon
)
)