code: public List<String> getUsernameAttributes() throws GuacamoleException {
          return environment.getProperty(
              LDAPGuacamoleProperties.LDAP_USERNAME_ATTRIBUTE,
              Collections.singletonList("uid")
          );
      }
docs: Returns all username attributes which should be used to query and bind
  users using the LDAP directory. By default, this will be "uid" - a
  common attribute used for this purpose.
  
  @return
  The username attributes which should be used to query and bind users
  using the LDAP directory.
  
  @throws GuacamoleException
  If guacamole.properties cannot be parsed.