code: public void initialize() {
          /*
           * Use a set to ensure we ignore duplicates.
           */
          val attributes = new HashSet<String>();
          LOGGER.debug("Initializing LDAP attribute configuration...");
          if (StringUtils.isNotBlank(this.principalIdAttribute)) {
              LOGGER.debug("Configured to retrieve principal id attribute [{}]", this.principalIdAttribute);
              attributes.add(this.principalIdAttribute);
          }
          if (this.principalAttributeMap != null && !this.principalAttributeMap.isEmpty()) {
              val attrs = this.principalAttributeMap.keySet();
              attributes.addAll(attrs);
              LOGGER.debug("Configured to retrieve principal attribute collection of [{}]", attrs);
          }
          if (authenticator.getReturnAttributes() != null) {
              val authenticatorAttributes = CollectionUtils.wrapList(authenticator.getReturnAttributes());
              if (!authenticatorAttributes.isEmpty()) {
                  LOGGER.debug("Filtering authentication entry attributes [{}] based on authenticator attributes [{}]", authenticatedEntryAttributes, authenticatorAttributes);
                  attributes.removeIf(authenticatorAttributes::contains);
              }
          }
          this.authenticatedEntryAttributes = attributes.toArray(ArrayUtils.EMPTY_STRING_ARRAY);
          LOGGER.debug("LDAP authentication entry attributes for the authentication request are [{}]", (Object[]) this.authenticatedEntryAttributes);
      }
docs: Initialize the handler, setup the authentication entry attributes.