Manually installing root certificate on macOS

NOTE: The following is based on macOS Yosemite 10.10.5. Other OS versions will have similar settings but they may not be worded the same or may be in slightly different places.

1. Go to Apps > SSL Inspector > Configuration and click the Download Root Certificate button. Save the root_authority.crt file.
   
   
   
2. Open up Keychain Access by searching it on Spotlight (clicking the Magnifying glass located on the upper right corner).
   
   
   
3. Select File > Import Items. Navigate to the file downloaded. Select System as "Destination Keychain".
   
   
   
4. Enter password when prompted.  
   
   
5. Logoff to take effect.
   
   
6. On some macOS versions you also need to do the following:
   • Right click on the certificate in Keychain Access and select Get Info
   • Expand the Trust section
   • Under When using this certificate select Always Trust.