The two files you need are a PEM encoded SSL certificate and private key. PEM encoded certs and keys are Base64 encoded text with start/end delimiters that look like -----BEGIN RSA PRIVATE KEY----- or similar.
To create an SSL certificate you first need to generate a private key and a certificate signing request, or CSR (which also contains your public key).You can do this in a variety of ways, but here’s how in OpenSSL.
openssl req -newkey rsa:2048 -new -nodes -keyout key.pem -out csr.pem
This will cause you to enter an interactive prompt to generate a 2048-bit RSA private key and a CSR that has all the information you choose to enter at the prompts. (Common Name is a legacy location where domain names used to go, but modern browsers require an extension called SubjectAlternativeName now. However, when submitting to a CA they will put CN values in SAN) Once you’ve done this you would normally submit this CSR to a trusted certificate authority and once they’ve validated your request you would receive a certificate.
If you don’t care about your certificate being trusted (usually the case for development purposes) you can just create a self-signed certificate. To do this, we can use almost the same line, but we’ll pass some extra parameters. The interactive prompt doesn’t support Subject Alternative Name (SAN), which is required in most modern clients, so we pass it on the CLI via the -addext flag. You’ll need to change mydnsname.com to the right name for your uses. Be sure to keep DNS: though!
openssl req -newkey rsa:2048 -new -nodes -x509 -days 3650 -keyout key.pem -out cert.pem -addext "subjectAltName = DNS:mydnsname.com"
This will give you a cert (valid for 10 years) and key pair that you can use in the code snippet you posted.