docs: protected Assertion buildCasAssertion(final Authentication authentication,
                                            final Service service,
                                            final RegisteredService registeredService,
                                            final Map<String, List<Object>> attributesToCombine) {
          val attributes = registeredService.getAttributeReleasePolicy().getAttributes(authentication.getPrincipal(), service, registeredService);
          val principalId = registeredService.getUsernameAttributeProvider().resolveUsername(authentication.getPrincipal(), service, registeredService);
          val principal = new AttributePrincipalImpl(principalId, (Map) attributes);
          val authnAttrs = new LinkedHashMap<>(authentication.getAttributes());
          authnAttrs.putAll(attributesToCombine);
          return new AssertionImpl(principal, DateTimeUtils.dateOf(authentication.getAuthenticationDate()),
              null, DateTimeUtils.dateOf(authentication.getAuthenticationDate()),
              (Map) authnAttrs);
      }