使用Xcode給iPhone做虛擬地址，或者開發時，編譯時有時會遇到證書相關的錯誤：
Warning: unable to build chain to self-signed root for signer "Mac Developer: Dylan M (*******)"
解決方法：
1. 首先可以嘗試Lock all cerficates
a. 打開 Keychain Access
b. File->Lock All Keychains
c. 運行Xcode的工程，訪問到證書時重新輸入密碼
2. 如果第一種方法失敗，按下面的提示去下載一個證書，然后clean Xcode的工程，重新編譯，通過
If none of the above works, download the WWDR Intermediate Certificate and drag and drop into your 'System' keychain. Don't put it in 'login' - I tried that myself and it did nothing to help me. Try to avoid changing the trust settings of your certificates, Xcode gave me a warning when it saw I had modified my development certificate's trust settings.