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)){
          ......
        }
     }

方法是这样的，

httpClient.DefaultRequestHeaders.Authorization =
    new AuthenticationHeaderValue("Bearer", "Your Oauth token");

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

use UTF8选项

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

我在寻找一个好的方法来处理这个问题，我也在考虑同样的问题。希望这个答案能帮助到每个和我一样有同样问题的人。

using (var client = new HttpClient())
{
    var url = "https://www.theidentityhub.com/{tenant}/api/identity/v1";
    client.DefaultRequestHeaders.Add("Authorization", "Bearer " + accessToken);
    var response = await client.GetStringAsync(url);
    // Parse JSON response.
    ....
}

参考来自https://www.theidentityhub.com/hub/Documentation/CallTheIdentityHubApi

使用System.Net.Http程序集的AuthenticationHeaderValue类

public AuthenticationHeaderValue(
    string scheme,
    string parameter
)

我们可以像这样设置或更新httpclient现有的授权头:

httpclient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", TokenResponse.AccessToken);