Used by the internal {@link #doAuthenticate} implementation to ensure that the {@code realms} property
has been set. The default implementation ensures the property is not null and not empty.
@throws IllegalStateException if the {@code realms} property is configured incorrectly.
Used by the internal {@link #doAuthenticate} implementation to ensure that the {@code realms} property has been set. The default implementation ensures the property is not null and not empty.
@throws IllegalStateException if the {@code realms} property is configured incorrectly.