Since https://issues.redhat.com/browse/WFCORE-5464, WildFly can resolve its expression properties from either system property or environment variables.
It provides a simple mapping as described in https://docs.wildfly.org/26.1/Admin_Guide.html#Expression_Resolution.

For consistence, that would be great if Elytron could support the same feature by updating its org.wildfly.security.jose.util.SystemPropertiesJsonParserFactory.SystemEnvProperties to use the same mapping.

As an example, this would allow to specify the OIDC provider url is a simple fashion.

In `oidc.json`, I would set:

  "provider-url": "${oidc.provider-url}",

and when I would run WildFly, I could use either the `oidc.provider-url` System property or the `OIDC_PROVIDER_URL` environment variable.

This would simplify the deployment of OIDC on OpenShift to use simple environment variables.