protected boolean isUserNameAttributeConfigured() {
        return unmappedUsernameAttribute != null;
    }
Indicates whether the value from {@link #getConfiguredUserNameAttribute()}
was configured explicitly.  A return value of {@code false} means
that the value from {@link #getConfiguredUserNameAttribute()} is a
default, and should not be used over a username passed in the query.

@return {@code true} If the 'unmappedUsernameAttribute' property was
set explicitly, otherwise {@code false}
core/cas-server-core-authentication-api/src/main/java/org/apereo/cas/authentication/attribute/AbstractQueryPersonAttributeDao.java