Secure access is sometimes necessary and useful for some features of the system. In these circumstances it’s worth installing a valid certificate.
Go to system > certificates, enter the details and click ‘Save and Generate CSR’.
Use the CSR to request a certificate from a trusted supplier. Once you’ve recieved it, make sure it is PEM format before proceeding.
Using the same page, paste the certificate at the top of the CRT text box followed by any intermediate certificates before clicking ‘Save Certificate’.
Go to system > shutdown / reboot and click ‘Reboot’ when convenient.