wp package install wp-cli/restful – fails

Hi guys.

What am I missing with this:

-> $ wp package install wp-cli/restful
Error: The “https://wp-cli.org/package-index/packages.json” file could not be downloaded: SSL operation failed with code 1. OpenSSL Error messages:
error:0A000086:SSL routines::certificate verify failed
Failed to enable crypto
Failed to open stream: operation failed

I’m doing this on Fedora where ‘wp-cli’ installs as rpm package from default repos.

many thanks, L.