这不是这种情况是因为微软使用了一些政策。

That's not the case because of some policies Microsoft uses.

如果用户登录Windows Live ID，他将会是自动登录所有相关属性，例如：如果用户登录Skydrive，他也将登录Hotmail和Spaces，但不会登录MSN，因为它是一个不同的品牌。单击MSN上的登录 -link将在不询问密码的情况下签到他（如果他刚刚登录，如果他刚刚签名，则必须重新输入密码）。

If a user signs in to Windows Live ID, he will be automatically signed in to all related properties, for example: if a user signs in to Skydrive, he'll be signed in to Hotmail and Spaces as well, but not to MSN as it's a different brand. Clicking the sign in-link on MSN will sign him in without asking for his password (if he just signed in, if he has signed in a while ago he has to re-enter his password).

你为什么要实现它？