code: protected Authorizable resolveAuthorizable(final String authorizableId) throws RepositoryException {
  
          final Session session = getAdminSession();
          final UserManager userManager = ((JackrabbitSession) session).getUserManager();
          final Authorizable authorizable = userManager.getAuthorizable(authorizableId);
          assertNotNull("Could not resolve " + authorizableId, authorizable);
          return authorizable;
      }
docs: Resolves a name to an {@link Authorizable}. The name can be of a user or a group. The resulting authroziable can
  be of type {@link org.apache.jackrabbit.api.security.user.User} or {@link org.apache.jackrabbit.api.security.user.Group}
  and has to be checked and cast accordingly. The method will fail with an {@link AssertionError} if no such
  authorizable exists.
  
  @param authorizableId
  the id of the authorizable
  
  @return the resolved {@link org.apache.jackrabbit.api.security.user.Authorizable}. It is either a {@link
  org.apache.jackrabbit.api.security.user.Group} or a {@link org.apache.jackrabbit.api.security.user.User}.
  
  @throws RepositoryException
  if the name was not found