Ensured the correct CA key and CA certificate is used during signing process...

This ensures that the correct CA key and CA certificate is used during signing process. It's been working based on default assumptions from the OpenSSL configuration, but it's worth being explicit when doing these operations.

Also removed a duplicate -sha256 parameter to one of the OpenSSL calls.

This is by no means a critical fix for anything, the current code works. It just ensures that we don't make accidental mistakes during signing.