Re: fo:external-graphic src="https:..."

Write Channel Closed, possible SSL handshaking or trust failure

Check whether the URL you want to access requires a client certificate
or some other presentation of client credentials. If so, you can't do
much short of hacking the FOP source for directly accessing the image.
There may be other possiblities, like an expired or misnamed server
certificate, ask any SSL guru near you.

Do you know how to set up the environment so it can handle this kind of
image?

Search the FOP and perhaps the Cocoon list archives for "HTTPS", or ask
on the Cocoon user list. This is now quite off-topic for this list.