try
window.open('https\://id.twitch.tv/oauth2/authorize?response_type=code&client_id=7d64ygbjjq2hk7z9lmtcdv7ta8a6i8&redirect_uri=' + encodeURIComponent('http://localhost/auth/'),'oAuth','width=490,height=850')
Similar to this example Twitch Implicit Auth Example