docs: @Override
      public String getProxyTicket(String service) {
          Assert.hasText(service, "service cannot not be null or blank");
          Assertion assertion = assertionProvider.getAssertion();
  
          AttributePrincipal principal = assertion.getPrincipal();
          if (principal == null) {
              throw new IllegalStateException(String.format(EXCEPTION_MESSAGE, AttributePrincipal.class.getSimpleName()));
          }
  
          return principal.getProxyTicketFor(service);
      }