微信获取时间戳，和过期日期

using System;

namespace Siia.WxPlatform.Web.Weixin.Helpers
{
    /// <summary>
    /// 微信 API 工具类
    /// </summary>
    public class ApiUtility
    {
        public static int GetTimeStamp
        {
            get
            {
                //var startTime = TimeZone.CurrentTimeZone.ToLocalTime(new DateTime(1970, 1, 1));
                var startTime =  TimeZoneInfo.ConvertTime(new DateTime(1970, 1, 1), TimeZoneInfo.Local);//等价的建议写法
                return (int)(DateTime.Now - startTime).TotalSeconds;
            }
        }
        /// <summary>
        /// 获取过期时间
        /// </summary>
        /// <param name="expireInSeconds">有效时间（秒）</param>
        /// <returns></returns>
        public static DateTimeOffset GetExpireTime(int expireInSeconds)
        {
            return DateTime.Now.Add(GetExpiryTimeSpan(expireInSeconds));//提前x分钟重新获取
        }
        /// <summary>
        /// 获取过期 TimeSpan
        /// </summary>
        /// <param name="expireInSeconds">有效时间（秒）</param>
        /// <returns></returns>
        public static TimeSpan GetExpiryTimeSpan(int expireInSeconds)
        {
            if (expireInSeconds > 3600)
            {
                expireInSeconds -= 600;//提前10分钟过期
            }
            else if (expireInSeconds > 1800)
            {
                expireInSeconds -= 300;//提前5分钟过期
            }
            else if (expireInSeconds > 300)
            {
                expireInSeconds -= 30;//提前1分钟过期
            }
            return TimeSpan.FromSeconds(expireInSeconds);
        }
    }
}