nginx 反向代理后，服务器生成的邮件验证码，不匹配的问题。
参考资料：http://www.gunaatita.com/Blog/Invalid-Token-Error-on-Email-Confirmation-in-Aspnet-Identity/1056
Reason #2 : The Confirmation token (UserManager.GenerateEmailConfirmationToken) is generated on one server and the mail confirmation code is on another server.
Solution : As confirmation token is generated using machine key and security stamp, so the machine key should be consistent on both server. So add same machineKey under system.web in configuration file of both the application as below:
<system.web>
</system.web>