一、在pageload方法中獲取code

    var code = GetCode();
    private string GetCode()
    {
        return HttpContext.Current.Request["code"];
    }

二、如果code為空，需要重定向到微信獲取code

//當前頁面對應的外網地址
            string redirect_url = "http://6018.ynedut.cn/PpWordOrder/default.aspx";
                redirect_url 
 
= HttpUtility.UrlEncode(redirect_url);
                var url = WeixinOauth2.GetCodeUrl(redirect_url); 
                HttpContext.Current.Response.Redirect(url);
                return;
            }
    #region ****************獲取codeurl****************
    /// <summary>
    /// 獲取codeurl
    /// </summary>
 

    /// <param name="redirectUri"></param>
    /// <returns></returns>
    public static string GetCodeUrl(string redirectUri)
    {
        return string.Format(
            "https://open.weixin.qq.com/connect/oauth2/authorize?appid={0}&redirect_uri={1}&response_type=code&scope=snsapi_userinfo&agentid={3}&state={2}#wechat_redirect
 
",
            PubConstant.AppId, redirectUri, new Random().Next(1000, 200000).ToString(),
            PubConstant.AgentId);
    }

    #endregion

三、根據code獲取用戶信息

　　註：code的有效時間為10分鐘，並且只能使用一次，所以這裏建議在load方法裏直接獲取用戶信息，並寫入cookie中

    /// <summary>
    /// 獲取用戶信息
    /// </summary>
    /// <param name="code"></param>
    /// <returns></returns>
    public static UserInfo GetUserInfo(string code)
    {
        var token = GetToken();
        var url = String.Format("https://qyapi.weixin.qq.com/cgi-bin/user/getuserinfo?access_token={0}&code={1}", token,
            code);
        string strResponse = HttpHelper.HttpGet(url);
        return JsonConvert.DeserializeObject<UserInfo>(strResponse);
    }
public class UserInfo
{
    public string UserId { get; set; }
    public string DeviceId { get; set; }
    [JsonProperty("user_ticket")]
    public string User_ticket { get; set; }
    [JsonProperty("expires_in")]
    public string Expires_in { get; set; }
}

    /// <summary>
    /// 獲取用戶詳細信息（包含了獲取用戶信息操作）
    /// </summary>
    /// <param name="code"></param>
    /// <returns></returns>
    public static UserDetailInfo GetUserDetailInfo(string code)
    {
        var userInfo = GetUserInfo(code);
        var url = String.Format(
            "https://qyapi.weixin.qq.com/cgi-bin/user/getuserdetail?access_token={0}", GetToken());
        JObject obj = new JObject();
        obj["user_ticket"] = userInfo.User_ticket;
        var postDataStr = obj.ToString();
        string strResponse = HttpHelper.HttpPost(url, postDataStr);
        return JsonConvert.DeserializeObject<UserDetailInfo>(strResponse);
    }
public class UserDetailInfo
{
    /// <summary>
    /// 成員UserID
    /// </summary>
    [JsonProperty("userid")]
    public string UserId { get; set; }

    /// <summary>
    /// 成員姓名
    /// </summary>
    [JsonProperty("name")]
    public string Name { get; set; }

    /// <summary>
    /// 成員所屬部門
    /// </summary>
    [JsonProperty("department")]
    public List<int> Department { get; set; }

    /// <summary>
    /// 職位信息
    /// </summary>
    [JsonProperty("position")]
    public string Position { get; set; }

    /// <summary>
    /// 成員手機號，僅在用戶同意snsapi_privateinfo授權時返回
    /// </summary>
    [JsonProperty("mobile")]
    public string Mobile { get; set; }

    /// <summary>
    /// 性別。0表示未定義，1表示男性，2表示女性
    /// </summary>
    [JsonProperty("gender")]
    public string Gender { get; set; }

    /// <summary>
    /// 成員郵箱，僅在用戶同意snsapi_privateinfo授權時返回
    /// </summary>
    [JsonProperty("email")]
    public string Email { get; set; }

    /// <summary>
    /// 頭像url。註：如果要獲取小圖將url最後的”/0”改成”/64”即可
    /// </summary>
    [JsonProperty("avatar")]
    public string Avatar { get; set; } 

}

Asp.net 微信企業號網頁開發流程