Unable to Establish Secure Connection to idmsa.apple.com

Matt Godden:

If you’re using #macOS #HighSierra or #Sierra, #iCloud has stopped working / can’t log in, and you can’t access iCloud.com in Safari - here’s a solution.

Install the Apple IST CA 2 - G1 certificate, and everything will work again.

Previously:

• Some Web Sites Will Stop Working With El Capitan and Older
• Beware Apple Security Certificates After October 24
• Previously Downloaded OS X Installers No Longer Work
• More Mac App Store Certificate Problems
• WWDR Intermediate Certificate Expiration