##Windows##
set OPENSSL_CONF=openssl.cnf
##Linux###
export OPENSSL_CONF=openssl.cnf
##Windows  or  Linux##
openssl x509 -req -days 760 -in Client.csr -CA RootCA.crt -CAkey RootCA.pem  -CAcreateserial -out Client.crt -extfile  openssl.cnf -extensions usr_cert -sha256