code: @Override
      public Set<Principal> getPrincipals(final HttpServletRequest request) {
          LOGGER.debug("Checking for principals using {}", ContainerRolesPrincipalProvider.class.getSimpleName());
  
          if (request == null) {
              LOGGER.debug("Servlet request was null");
  
              return emptySet();
          }
  
          if (roleNames == null) {
              LOGGER.debug("Role names Set was never initialized");
  
              return emptySet();
          }
  
          final Iterator<String> iterator = roleNames.iterator();
          final Set<Principal> principals = new HashSet<>();
  
          while (iterator.hasNext()) {
              final String role = iterator.next().trim();
  
              if (request.isUserInRole(role)) {
                  LOGGER.debug("Adding container role as principal: {}", role);
  
                  principals.add(new ContainerRolesPrincipal(role));
              }
          }
  
          return principals;
      }
docs: /*
  (non-Javadoc)
  @see
  org.fcrepo.auth.PrincipalProvider#getPrincipals(javax.servlet.http.HttpServletRequest)