Navigate to the folder where you saved the PEM certificate and double-click on it:
Figure 13 - Selecting the certificate file
This will open the Keychain app. Select Add in the pop-up window:
Figure 14 - Adding the certificate
Enter your password to confirm the action:
Figure 15 - Entering the password
Navigate to the Applications menu and double-click the Utilities icon:
Figure 16 - Locating Utilities
In the Utilities subfolder locate and double-click the Keychain Access icon:
Figure 17 - Opening Keychain Access
The Keychain Access window will open. Under the Default Keychains > login section locate an entry called Default Certification Authority and select it:
Figure 18 - Opening the Default Certification Authority settings
In the newly opened settings window navigate to the Trust section and set all parameters in this section to "Always Trust":
Figure 19 - Editing the Default Certification Authority settings
Enter your password to save the new settings:
Figure 20 - Entering the password to update the settings
The certificate is successfully installed.