Fixing the "Failed to connect to authentication server" error in GlobalProtect VPN for Mac

If your Mac is running macOS El Capitan (v10.11) you will get this error message when you first try to connect to GlobalProtect VPN. To fix it, you will need to adjust your security settings.

1. In the upper right corner of your Mac, click the magnifying glass to perform a spotlight search for Keychain Access. Double-click the top search result to open it.           
2. In the section labelled Keychains select login, and in the section labelled Category select Certificates. Then double-click inCommon RSA Server CA to view its properties. 

• If the certificate isn't there, download it: InCommon RSA Server CA 2.cer and USERTrust RSA Certification Authority.cer​​​​. Then go to your Downloads folder and double-click it to install them. 

1. To the left of Trust, click the arrow to open the properties. Next to When using these certificates , change the setting from Use system defaults to Always Trust.  Certificate names are now "InCommon RSA Server CA 2.cer"  and "USERTrust RSA Certification Authority.cer"
   
2. Close this window, and when prompted, enter the admin password for your Mac.
3. Connect to GlobalProtect VPN.