Thank you, Bartosz, for your answer.
I agree that I have to store passwords somehow in a server config. Actually, I am already using Elytron to store passwords - e.g. for the user to connect to the datasource - and it has worked well so far.
Let me try to clarify my issue.
I would like to set up an SSL context for the communication between Wildfly and the datasource. To do so, Wildfly needs to have a keystore - with the client key and certificate - and a truststore - with the CA certificate which signed the datasource certificate. These stores are password-protected. Thanks to Elytron, no password in plain text in standalone/configuration/standalone.xml: I agree.
The problem is that this is not enough: no way to bind the datasource with such a configuration. There still needs the passing of the options -Djavax.net.ssl.trustStore, -Djavax.net.ssl.trustStorePassword, -Djavax.net.ssl.keyStore and -Djavax.net.ssl.keyStorePassword to the JVM, in the bin/standalone.conf file.
=> why so? And how to avoid it, if possible?
I hope I have made my point clearer now.
Good bye,
AC