SharePoint 允许您设置登录用户的身份验证.您可以为网站成员分配权限.如您所愿，您可以赋予付费用户访问网站的***.
为了使它更好，您可以使用SharePoint Designer，它使您可以拖动登录"文本框来检查标识.

SharePoint allows you to set authentication for login users. You are enabled to assign permissions for websites Members. As you wish, you can endow people who have paid with the freedom to access your website.
To make it better, you can make use of SharePoint Designer, which enables you to drag Login textbox to have a check on the identification.