use UTF8选项

request.DefaultRequestHeaders.Authorization = 
new AuthenticationHeaderValue(
    "Basic", Convert.ToBase64String(
        System.Text.Encoding.UTF8.GetBytes(
           $"{yourusername}:{yourpwd}")));

这可能有助于设置标题:

WebClient client = new WebClient();

string authInfo = this.credentials.UserName + ":" + this.credentials.Password;
authInfo = Convert.ToBase64String(Encoding.Default.GetBytes(authInfo));
client.Headers["Authorization"] = "Basic " + authInfo;

对于性能和端口耗尽问题，重用HttpClient实例是一个很好的实践，而且因为没有一个答案给出了这个解决方案(甚至会把你引向糟糕的实践:)，所以我在这里放了一个链接，指向我对类似问题的回答:

https://stackoverflow.com/a/40707446/717372

一些关于如何正确使用HttpClient的源代码:

https://aspnetmonsters.com/2016/08/2016-08-27-httpclientwrong/ https://blogs.msdn.microsoft.com/alazarev/2017/12/29/disposable-finalizers-and-httpclient/

你也可以使用下面的例子，它使用IHttpClientFactory:

    readonly IHttpClientFactory _httpClientFactory;
    
    public HTTPClientHelper(IHttpClientFactory httpClientFactory, string clientName = null)
    {
        this._httpClientFactory = httpClientFactory;
    }

    public Task<T> GetAsync(string url, string token) {

        var client = _httpClientFactory.CreateClient(_clientName);

        client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(JwtBearerDefaults.AuthenticationScheme, token);

        using (HttpResponseMessage response = await _client.GetAsync(url)){
          ......
        }
     }

6年过去了，但为了帮助别人，我加了这个。

https://www.codeproject.com/Tips/996401/Authenticate-WebAPIs-with-Basic-and-Windows-Authen

var authenticationBytes = Encoding.ASCII.GetBytes("<username>:<password>");
using (HttpClient confClient = new HttpClient())
{
  confClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", 
         Convert.ToBase64String(authenticationBytes));
  confClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue(Constants.MediaType));  
  HttpResponseMessage message = confClient.GetAsync("<service URI>").Result;
  if (message.IsSuccessStatusCode)
  {
    var inter = message.Content.ReadAsStringAsync();
    List<string> result = JsonConvert.DeserializeObject<List<string>>(inter.Result);
  }
}

使用c# HttpClient设置基本身份验证。下面的代码为我工作。

   using (var client = new HttpClient())
        {
            var webUrl ="http://localhost/saleapi/api/";
            var uri = "api/sales";
            client.BaseAddress = new Uri(webUrl);
            client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
            client.DefaultRequestHeaders.ConnectionClose = true;

            //Set Basic Auth
            var user = "username";
            var password = "password";
            var base64String =Convert.ToBase64String( Encoding.ASCII.GetBytes($"{user}:{password}"));
            client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic",base64String);

            var result = await client.PostAsJsonAsync(uri, model);
            return result;
        }