The reply from curl:
Array
(
[url] => https://id.twitch.tv/oauth2/token?client_id=***f&client_secret=***&grant_type=client_credentials
[content_type] => text/html
[http_code] => 400
[header_size] => 150
[request_size] => 271
[filetime] => -1
[ssl_verify_result] => 0
[redirect_count] => 0
[total_time] => 0.816135
[namelookup_time] => 0.028959
[connect_time] => 0.188394
[pretransfer_time] => 0.65653
[size_upload] => 0
[size_download] => 122
[speed_download] => 149
[speed_upload] => 0
[download_content_length] => 122
[upload_content_length] => -1
[starttransfer_time] => 0.816076
[redirect_time] => 0
[redirect_url] =>
[primary_ip] => 35.82.117.112
[certinfo] => Array
(
)
[primary_port] => 443
[local_ip] => 185.110.173.101
[local_port] => 50338
)