Create the symlink.
ln -s /etc/openxpki/ca/ca-one/ca-signer-1.key /etc/openxpki/ca/ca-one/ca-signer-1.pem
ln -s /etc/openxpki/ca/ca-one/scep-1.key /etc/openxpki/ca/ca-one/scep-1.pem
ln -s /etc/openxpki/ca/ca-one/vault-1.key /etc/openxpki/ca/ca-one/vault-1.pem