ASP.NET Core2静默获取微信公众号的用户OpenId实例代码

/// <summary>
/// 业务基类
/// </summary>
public class BasicController:Controller
{
	//当前用户openId
	protected string CurrentUserOpenId { set; get; }

	public BasicController()
	{
		//从Cookie中获取当前用户的openId
		var cookie = Cookies.GetCookieByUser();
		//如果没有，则导航到指定提示页，需要用户关闭后重新进入
		if (string.IsNullOrEmpty(cookie))
		{
			System.Web.HttpContext.Current.Response.Redirect("/VxinWeb/Index");
			return;
		}

		CurrentUserOpenId = cookie;
	}
}

/// <summary>
/// 此页面用于对外微信菜单地址，用于获取用户openId
/// 这是本系统网页的入口
/// </summary>
public class VxinWebController : Controller
{
	public ActionResult Index()
	{
		//获取当前进到本系统的微信用户的openid
		//该请求从微信那边过来
		if (Request.QueryString["code"] != null)
		{
			var code = Request.QueryString["code"].ToString();
			var openId = VxinUtils.GetOpenID(code);
			if (openId == null)//没有获取到openId
			{
				//返回当前视图，需要提示用户关闭窗口，尝试重新进入
				return View();
			}
			//将openId放入cookie，放到cookie之前需将openId进行加密，取出来后再解密
			Cookies.SetUserToCookie(openId);
			return RedirectToAction("Index", "Home");
		}
		return View();
	}
}

/// <summary>
/// 微信公众号工具类
/// </summary>
public class VxinUtils
{

	/// <summary>
	/// 微信token
	/// </summary>
	public static string WeiXinToken { get { return ConfigurationManager.AppSettings["WeiXinToken"].ToString(); } }

	/// <summary>
	/// 微信appID
	/// </summary>
	public static string AppID { get { return ConfigurationManager.AppSettings["AppID"].ToString(); } }


	/// <summary>
	/// 微信Aappsecret
	/// </summary>
	public static string Appsecret { get { return ConfigurationManager.AppSettings["Appsecret"].ToString(); } }


	/// <summary>
	/// 获得access_token地址
	/// </summary>
	public static string Access_token_URL { get { return string.Format("https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid={0}&secret={1}", AppID, Appsecret); } }

	/// <summary>
	/// 通过code换取网页授权access_token地址
	/// </summary>
	public static string Web_Access_token_URL { get { return string.Format("https://api.weixin.qq.com/sns/oauth2/access_token?appid={0}&secret={1}&grant_type=authorization_code&code=", AppID, Appsecret); } }


	/// <summary>
	/// 微信菜单创建提交地址
	/// </summary>
	public static string MENU_POST_URL { get { return "https://api.weixin.qq.com/cgi-bin/menu/create?access_token="; } }


	/// <summary>
	/// 微信获取用户分组地址
	/// </summary>
	public static string Group_Get_Url { get { return "https://api.weixin.qq.com/cgi-bin/groups/get?access_token="; } }


	/// <summary>
	/// 微信修改用户分组地址
	/// </summary>
	public static string Group_Update_Url { get { return "https://api.weixin.qq.com/cgi-bin/groups/members/update?access_token="; } }



	/// <summary>
	/// 微信获取用户所属分组地址
	/// </summary>
	public static string Group_GetUserGroup_Url { get { return "https://api.weixin.qq.com/cgi-bin/groups/getid?access_token="; } }

	/// <summary>
	/// 拉取用户信息(需scope为 snsapi_userinfo)
	/// 如果网页授权作用域为snsapi_userinfo，则此时开发者可以通过access_token和openid拉取用户信息了。
	/// https://api.weixin.qq.com/sns/userinfo?access_token=ACCESS_TOKEN&openid=OPENID&lang=zh_CN
	/// </summary>
	public static string GetUserUserinfo_Url { get { return "https://api.weixin.qq.com/sns/userinfo?lang=zh_CN&access_token="; } }


	/// <summary>
	/// 获取用户的OpenId
	/// </summary>
	/// <param name="code"></param>
	/// <returns></returns>
	public static string GetOpenID(string code)
	{
		var openid = "";
		using (var wl = new WebClient())
		{
			wl.Headers.Add(HttpRequestHeader.Accept, "json");
			wl.Headers.Add(HttpRequestHeader.ContentType, "application/json;charset=UTF-8");
			wl.Headers.Add(HttpRequestHeader.UserAgent, "Mozilla/4.0");
			wl.Encoding = Encoding.UTF8;
			openid = wl.DownloadString(Web_Access_token_URL + code);
		}
		if (!string.IsNullOrEmpty(openid))
		{
			var token = JObject.Parse(openid).SelectToken("openid");
			if (token != null)
				openid = token.ToString();
		}
		return openid;
	}

}