public static Access_token GetAccessToken()

{

    string formatString = String.Format("https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid={0}&secret={1}", AppId, AppSecret);

    Access_token res = new Access_token();

    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(formatString);

    request.Method = "GET";

    request.ContentType = "text/html;charset=UTF-8";

    HttpWebResponse response = (HttpWebResponse)request.GetResponse();

    Stream myResponseStream = response.GetResponseStream();

    StreamReader myStreamReader = new StreamReader(myResponseStream, Encoding.GetEncoding("utf-8"));

    string retString = myStreamReader.ReadToEnd();

    myStreamReader.Close();

    myResponseStream.Close();

    if (retString.IndexOf("") > )

    {

        Access_token token = new Access_token();

        token = JsonHelper.ParseFromJson<Access_token>(retString);

        res.access_token = token.access_token;

        res.expires_in = token.expires_in;

    }

    return res;

}

public class Access_token

{

    public Access_token()

    {

        //

        //TODO:用于验证Access_token是否过期实体

        //

    }

    string _access_token;

    string _expires_in;

    /// <summary>

    /// 获取到的凭证

    /// </summary>

    public string access_token

    {

        get { return _access_token; }

        set { _access_token = value; }

    }

    /// <summary>

    /// 凭证有效时间，单位：秒

    /// </summary>

    public string expires_in

    {

        get { return _expires_in; }

        set { _expires_in = value; }

    }

}

/// <summary>

/// 将JSON对象转换为Model

/// </summary>

/// <typeparam name="T"></typeparam>

/// <param name="szJson"></param>

/// <returns></returns>

public static T ParseFromJson<T>(string szJson)

{

    T obj = Activator.CreateInstance<T>();

    using (MemoryStream ms = new MemoryStream(Encoding.UTF8.GetBytes(szJson)))

    {

        DataContractJsonSerializer serializer = new DataContractJsonSerializer(obj.GetType());

        return (T)serializer.ReadObject(ms);

    }

}