Web API 如何请求基于Basic/Bearer 头的方式 C#

public void SetBasicAuthHeader(WebRequest request, String userName, String userPassword)
{
    string authInfo = userName + ":" + userPassword;
    authInfo = Convert.ToBase64String(Encoding.Default.GetBytes(authInfo));
    request.Headers["Authorization"] = "Basic " + authInfo;
}

public void FetchTasks(string url, string accessToken)
{
    var httpWebRequest = HttpWebRequest.CreateHttp(url);
    request.Headers.Add("Authorization", "Bearer "+accessToken);
    httpWebRequest.BeginGetResponse(new AsyncCallback(FinishedWebRequest), httpWebRequest);
}