The flags parameter allows to control the checking of digital signature
upon EntityDescriptor and EntitiesDescriptor nodes in SAML 2.0 metadata
files.
The default behaviour is to check all found signatures and to inherit
signature from EntitiesDescriptor to their children.
By only enabling checking of EntityDescrtiptor node signatures it's also
possible to only check signature at the EntityDescriptor level and so
only trust individual entities and not the aggregating provider.
Benjamin Dauvergne