C# HTTP基本身份验证凭据发送得太早

using System;
using System.Net;
using System.IO;

class Program
{
    static void Main()
    {
        string url = "https://example.com/api";
        string username = "your_username";
        string password = "your_password";

        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
        request.Method = "GET";

        // Check if server requires authentication
        if (request.GetResponse() is HttpWebResponse response && response.StatusCode == HttpStatusCode.Unauthorized)
        {
            // Server requires authentication, send credentials
            string credentials = Convert.ToBase64String(System.Text.Encoding.ASCII.GetBytes(username + ":" + password));
            request.Headers.Add("Authorization", "Basic " + credentials);

            // Retry the request
            response = (HttpWebResponse)request.GetResponse();
        }

        // Process the response
        using (StreamReader reader = new StreamReader(response.GetResponseStream()))
        {
            string responseText = reader.ReadToEnd();
            Console.WriteLine(responseText);
        }
    }
}