以下是一个使用AD B2C的非交互/无头身份验证并使用资源所有者密码凭证流程的代码示例：

using System;
using System.Net.Http;
using System.Threading.Tasks;
using Newtonsoft.Json;

public class Program
{
    public static async Task Main(string[] args)
    {
        // 配置AD B2C租户和应用程序的详细信息
        string tenantId = "your-tenant-id";
        string clientId = "your-client-id";
        string clientSecret = "your-client-secret";
        string policy = "your-policy-name";
        string scope = "your-scope";

        // 构建请求的参数
        var requestParams = new Dictionary
        {
            { "grant_type", "password" },
            { "client_id", clientId },
            { "client_secret", clientSecret },
            { "scope", scope },
            { "username", "your-username" },
            { "password", "your-password" },
        };

        // 构建请求的URL
        string requestUrl = $"https://{tenantId}.b2clogin.com/{tenantId}.onmicrosoft.com/{policy}/oauth2/v2.0/token";

        // 发送请求获取访问令牌
        using (var httpClient = new HttpClient())
        {
            var response = await httpClient.PostAsync(requestUrl, new FormUrlEncodedContent(requestParams));
            var responseContent = await response.Content.ReadAsStringAsync();
            
            // 解析响应内容
            var tokenResponse = JsonConvert.DeserializeObject(responseContent);
            
            if (tokenResponse != null && !string.IsNullOrEmpty(tokenResponse.AccessToken))
            {
                // 使用访问令牌调用API
                string apiUrl = "your-api-url";
                httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", tokenResponse.AccessToken);
                var apiResponse = await httpClient.GetAsync(apiUrl);
                var apiResponseContent = await apiResponse.Content.ReadAsStringAsync();

                Console.WriteLine(apiResponseContent);
            }
        }
    }

    public class TokenResponse
    {
        [JsonProperty("access_token")]
        public string AccessToken { get; set; }

        [JsonProperty("expires_in")]
        public int ExpiresIn { get; set; }

        [JsonProperty("token_type")]
        public string TokenType { get; set; }
    }
}

请注意，此示例代码仅用于说明目的。在实际环境中，应该进行错误处理、参数验证和安全性考虑。