Allow usage of properties to configure sasl server factories

There is some discussion on https://github.com/wildfly-security/wildfly-elytron/pull/264. In this case the issue is that we have a ChannelBindingSaslServerFactory (and same for client) which provides a callback handler to deal with the channel binding callbacks needed by Gs2SaslServerFactory and Gs2SaslClientFactory. This is fine for when people create their own SaslServerFactory, and use that to create a SaslServer.

However, if they want to call Sasl.createServer()/.createClient() they need to provide their own callback handler to deal with the channel binding types.

One option would be to allow the usage of properties for this configuration needed by the factories.

However, having slept on it, the callback handler passed in to Sasl.createXXX() would need to handle all callbacks. Is there a way to get a 'real' callback handler for a user wishing to instantiate clients/servers this way? Or is the intent that they have to write their own CBH?