I'm trying to request a certifiacte through SCEP service. I used openssl to generate key and CSR file. But I don't find a way to generate PKImessage send to scep server. Is it possible to use openssl cli to generate the message?
The simple answer is 'No'.
However, you could use sscep which is a free command-line tool that will send the request to your SCEP server.
It's available from https://github.com/certnanny/sscep. A complied version for Windows is available from here and I believe it's available for RPM based Linux distros too.