Create self signed certificate:
openssl req -new -x509 -sha256 -newkey rsa:2048 -nodes -keyout server.key -days 365 -out server.crt
Create new key:
openssl genrsa -out server.key 2048
Create new key and a certificate sign request:
openssl req -new -sha256 -newkey rsa:2048 -nodes -keyout server.key -out server.csr
Or use an existing key to create a certificate sign request:
openssl req -new -sha256 -key server.key -out server.csr
Verify the certificate: