curlopt_httpheader相当于c＃

I'm trying to convert a piece of php code to C#. But I can't find any sample of CURLOPT_HTTPHEADER equivalent in C#. In fact the code that I try to convert is here:

$churi = curl_init($uri);
curl_setopt($ch, CURLOPT_HTTPHEADER, array('apipass:'.$key)); 
$res = curl_exec($churi); 
$obj = json_decode($res);

Any help will be appreciated. Thanks

If you use HttpClient you can use the following code for adding custom request headers:

var key = "yourkey"
client.DefaultRequestHeaders.Add("apipass",key);

I hope this can help you