You don’t need authentication to access someone’s followers: https://github.com/justintv/Twitch-API/blob/master/v3_resources/follows.md#get-channelschannelfollows
If you wish to make a user follow a channel, that’s documented here: https://github.com/justintv/Twitch-API/blob/master/v3_resources/follows.md#put-usersuserfollowschannelstarget and requires the users_follows_edit scope.