Additional Apple devices must be authorized to use the iCloud Keychain service using a combination of the Apple ID password and another method. One method involves using an iCloud Security Code; the other method is to authorize access from another Apple device that has already been configured for the iCloud Keychain service.
If an issue disappears when a Safe Boot is successful, you must find and remove the third-party startup resource that caused the issue. The best way to isolate the problem is to start up the Mac in Verbose mode and then observe where the startup process fails. Verbose mode is initiated by holding down Command-V during system startup.
A standard user can connect to any non-WPA Enterprise Wi-Fi network via the Wi-Fi status menu. Because the system Keychain must be modified for WPA Enterprise connections, only an administrative user can establish these types of connections.
Key chains are used to store secrets such as resource passwords, digital certificates, and encryption keys. The keychain system can also securely store Safari AutoFill information, Internet Account settings, and secure text notes.