Crowd RemoteDirectory implementations should not throw RuntimeExceptions unless there is a catastrophic, system-wide, non-recoverable error

Some examples include throwing IllegalArgumentExceptions and UnsupportedOperationExceptions

Instead we should prefer throwing checked exceptions such as InvalidUser/InvalidGroup and ReadOnlyGroupException/OperationFailedException. The message of the method should be used to explain the underlying specific cause of the error as it is likely to get logged.

Runtime exceptions cause the entire ASG iteration over directories to fail-fast and, in most cases, bubble straight up to the UI and smacks the user with a 500 page.