Step 1 - create a config.txt file for the CSR :
[req] distinguished_name = req_distinguished_name req_extensions = v3_req prompt = no [req_distinguished_name] C = US ST = Illinois L = Some City O = Company Name OU = IT Dept CN = www.website.com [v3_req] keyUsage = keyEncipherment, dataEncipherment extendedKeyUsage = serverAuth subjectAltName = @alt_names [alt_names] DNS.1 = website.com
Step 2 - create the CSR file:
openssl req -new -out certificate.csr -newkey rsa:2048 -nodes -sha256 -keyout certificate.key -config config.txt
Done!
More info here: https://www.siteground.co.uk/kb/how_to_generate_a_csr/