Support for the ``allow_extra_attributes`` key in the context was introduced

in Symfony 3.3.

By default, additional attributes that are not mapped to the denormalized

objectwill be ignored by the Serializer component.Include a

``ClassMetadataFactory``whenconstructingthenormalizer and set the

``allow_extra_attributes``key of the deserialization context to ``false`` to

let the serializer throw an exceptionwhenadditional attributes are passed::

By default, additional attributes that are not mapped to the denormalized object

will be ignored by the Serializer component.If you prefer to throw an exception

whenthis happens, setthe``allow_extra_attributes`` context option to

``false``and provide an object that implements ``ClassMetadataFactoryInterface`