在访问 https://appleid.apple.com/account?&localang=CN-ZH 这个页面的时候，页面会ajax一个特殊的header请求，其中的X-Apple-I-FD-Client-Info信息是一个json对象，本gist是整理后的F值获取方式源码。

X-Apple-I-FD-Client-Info.js

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