Use an SSL certificate in macOS Server
The server can use an SSL certificate to identify itself electronically and communicate securely with users’ computers and other servers on the local network and the Internet.
You can use the self-signed certificate created for your server when you set it up, or a self-signed certificate you created. However, users’ apps won’t trust self-signed certificates and will display a messages asking if the user trusts your certificate. Using a signed certificate relieves users from the uncertainty and tedium of manually accepting your certificate in these messages. A man-in-the-middle spoofing attack is possible with a self-signed certificate.
Select Certificates in the Server app sidebar.
To use one certificate for all services, choose a certificate from the “Secure services using” pop-up menu.
To use different certificates for each service, choose Custom from the “Secure services using” pop-up menu, then choose an available certificate for each service.
If the pop-up menu doesn’t contain certificates, create a self-signed certificate. For instructions, see Create a self-signed certificate in macOS Server.
To use a previously generated SSL certificate, import it.
To disable secure connections, choose None.