Summary

Add op-mode command having ability to show private key in pem format as part of show pki certificate ...

Use case

Currently, we have show pki certificate <NAME> pem to render certificate in PEM format. But there isn't a way to render the private key for the certificate in PEM format.

The ability to render private key with show pki certificate <NAME> private pem allows for convenience of rendering a certificate and its private key in other services that are not natively available in VyOS -- for example, in a containerized service.

Additional information

There isn't much of additional security implication because the privilege used to actually access the certificate and privkey in /config/auth is same as the one to run show pki certificate ... -- or for example, accessing the private key in /tmp/haproxy if the system is configured with haproxy configuration with an active SSL certificate.