You can get Access Token as following
private static string WebResponseGet(string url)
{
HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create(url);
using (StreamReader reader = new StreamReader(webRequest.GetResponse().GetResponseStream()))
{
return reader.ReadToEnd();
}
}
private void GetToken(string code, string userId)
{
string accessToken = WebResponseGet(string.Format("https://graph.facebook.com/oauth/access_token?client_id={0}&redirect_uri={1}&client_secret={2}&code={3}", "API_Key", "Redirect URL", "API_Secret", code));
}