As discussed with Martin and Darran, temporarily add a Pem.generatePemX509Certificate() method that takes the ByteStringBuilder from Elytron as a parameter. This will prevent the need for modifying org.wildfly.extension.elytron.AdvancedModifiableKeyStoreDecorator when building Core with the latest Elytron SNAPSHOT version. Since org.wildfly.security.pem.Pem is private API, we can remove this new method later on.