after searching and fiddeling for quite sometime, sparkweb with openfire 3.8.2 and SSL requirement is finally working.
The connection settings in the sparkweb.html file to get sparkweb working with SSL (openfire set to "Required") are:
As the openfire and webserver are on the same machine, I just set the server to localhost. Technically I wouldn't need to connect with SSL, as it is on the same machine and only this jabber domain is offered to connect to with sparkweb. But to have openfire's security setting set to "SSL/TLS Required" (for use with external desktop clients) I am forced to do so. Calling sparkweb.html with https in the browser would secure (encrypt) the connection efficiently, in the above setup (openfire & webserver on the same machine).
If the jabber server and webserver would reside on 2 different networks, and the connection between each other should be encrypted, the connection type for sparkweb to the jabber server would have to be https with the reflecting port and server:jabberserverdomain.tld .
I hope this will help and encourage others to get it working.