Here’s the GetTwitchFollowers() function:
TwitchLib - TwitchAPI.cs - GetTwitchFollowers()
The function calls MakeGetRequest(), which is seen here:
TwitchLib - TwitchAPI.cs - MakeGetRequest()
The client id header is added directly tot he HttpWebRequest, so I should be good there. In addition, I pass it as a GET parameter to be safe (which I believe to be still valid).
Edit: post formatting, I accidentally linked GetFollowedUsers(), not GetTwitchFollowers(), sorry about that!