start.sh new_server & new_client explanation

[Jeredriq]

I don't really understand what is happening in new_server and new_client. It would be great if there was some explanation documentation about the sertificates.

I really don't understand what is going on here:
openssl x509 -req -days 3650 -in "${SERVER_DIR}/server.csr" -CAcreateserial \ -extfile <(sed "s/\$ENV::SERVER_NAME/${SERVER_NAME}/g" "${CWD}/certs/server.ext") \ -CAkey "${SERVER_DIR}/ca.key" -CA "${SERVER_DIR}/server_ca.pem" -out "${SERVER_DIR}/server.crt" cat "${SERVER_DIR}/server.crt" "${SERVER_DIR}/server_ca.pem" > "${SERVER_DIR}/server.chain.pem"

What are the uses for server.chain.pem and deviceid.chain.pem files. Why are we creating a serial? I know it is not an issue but a demand for explanation in ReadMe file. Thanks for the help.