A second state authority (Court of Appeals or Ministry of Foreign Affairs) verifies the signature of the first level state authority. This is called an apostille or legalization
Note bene: In France, unlike most countries in the world, two level 2 authorities are in charge of legalizations.
The Court of Appeals is responsible for legalizing documents for countries that have signed the Hague Convention, while the Ministry of Foreign Affairs is responsible for legalizing documents for countries that have not signed the Hague Convention.