string strContent = "?grant_type=password" +
            "&client_id=" + "xxx.xxxx" +
            "&client_secret=" + "secret"+
            "&username=" + "amitghosh@domain.com" +
            "&password=" + "pass&apitoken";


var o = new HttpClient();

var t = o.GetStringAsync("https://login.salesforce.com/services/oauth2/token"+strContent).Result