`openssl req -newkey rsa:2048 -nodes -keyout key.pem -x509 -days 365 -out certificate.pem`

or

call QP2TERM

openssl genrsa -des3 -out server.key 1024

openssl req -new -key server.key -out server.csr

cp server.key server.key.org

openssl rsa -in server.key.org -out server.key

Generate the Self-Signed Certificate with the command openssl x509 -req -days 365 -in server.csr -signkey server.key -out server.crt

The last optional command is to convert the certificate to a PKCS12 format with the command openssl pkcs12 -export -out exported.pfx -inkey server.key -in server.crt

Reference:

https://www.ibm.com/support/pages/how-create-self-signed-certificate-openssl