@Override
    public Set<String> getPossibleUserAttributeNames(final PersonAttributeDaoFilter filter) {
        return Set.copyOf(this.possibleUserAttributeNames);
    }
Map from query attribute names to data-layer attribute names to use when building the query. If an ordered Map is
passed in the order of the attributes will be honored when building the query.
If not set query attributes will be used directly from the query Map.

@param queryAttributeMapping the queryAttributeMapping to set
core/cas-server-core-authentication-api/src/main/java/org/apereo/cas/authentication/attribute/AbstractQueryPersonAttributeDao.java