This feature request is about adding a mechanism for making WSS4J (and possibly other projects relying on it) transparently use a Security Provider without globally installing it the JVM. This prevents side effects on other frameworks running within the same JVM and not wanting the BouncyCastle provider currently registered by WSS4J.
The idea is to register a provider acting as a proxy to a different and thread local scoped provider. The proxied provider reference would have to be set and cleaned up by the WSS4J consumers. The reference being thread local ensures different threads don't have access to it. When no proxied provider is set, the installed provider basically serves no algorithm / service.