During preparation for boot of a managed server the HC resolves expressions in portions of the domain and host configs that configure the server launch. But that expression resolution is unable resolve extension expressions (i.e. those that require an Elytron subsystem expression-resolver resource to resolve).

This is because ExpressionResolverExtension's like ElytronExpressionResolver require an OperationContext in order to resolve, but there is no OC available when the HC is preparing a server launch.

ElytronExpressionResolver is also able to resolve using a CapabilityServiceSupport, so adding a method to ExpressionResolver that passes in one (instead of OperationContext) may be a way to allow resolution.