while there exists API to check if a given Principal is backed by an Item in the repository (see ItemBasedPrincipal.getPath, we currently lack the ability to retrieve these principals by path. In other words the round trip is incomplete and forces consumers the workaround by involving user management API, which may or may not work depending on the implementation details of the underlying PrincipalProvider.
the suggested extension would (in correspondence to the recent search extensions) be made optional by adding a default implementation to the PrincipalProvider interface.
Alex Deparvu, will attach an initial patch. feedback both on the proposal and on the patch welcome as always.