安装p12私有证书，显示错误：
An error has occurred. Unable to import an item. The contents of this item cannot be retrieved. Missing .pem file
打开命令行，用以下命令安装即可:
security import priv_key.p12 -k ~/Library/Keychains/login.keychain
security import pub_key.pem -k ~/Library/Keychains/login.keychain
参考
https://stackoverflow.com/questions/6076448/an-error-has-occurred-unable-to-import-an-item-the-contents-of-this-item-canno
