Always know how to do... whatever using the cli.
-
Obtain the server key, server cert and intermediate cert in PEM format. I use letsencrypt.org, and so name my intermediate cert "letsencrypt-chain.crt". The system doesn't care what you use as a filename extension. I usually use ".key" for keys, and ".crt" for certs. In the case of the combo cert I used ".pem" just because...
-
Combine the server key and cert into a single file (in that order):
$ cat server-key.pem server-cert.pem > _.example.com-combo.pem
You can name things anything you want so long as you make sure the lighttpd uses those names