The full client_id is passed along with scope and state.
https://api.twitch.tv/kraken/oauth2/authorize?
response_type=code
&client_id=rkk6br1pkzoe85af80crvqpzbr7kl7f1
&redirect_uri=http://localhost/wordpress/wp-admin/admin.php?page=twitchpress
&scope=user_read+user_blocks_edit+user_blocks_read+user_follows_edit+channel_read+channel_editor+channel_commercial+channel_stream+channel_subscriptions+user_subscriptions+channel_check_subscription+chat_login+channel_feed_read+channel_feed_edit
&state=1%2Chttp%3A%2F%2Flocalhost%2Fwordpress2544747%2Cadmin