# Buggy code
def setup_security(
    self,
    allowed_serializers=None,
    key=None,
    cert=None,
    store=None,
    digest="sha1",
    serializer="json",
):
    """Setup the message-signing serializer.

    This will affect all application instances (a global operation).

    Disables untrusted serializers and if configured to use the ``auth``
    serializer will register the ``auth`` serializer with the provided
    settings into the Kombu serializer registry.

    Arguments:
        allowed_serializers (Set[str]): List of serializer names, or
            content_types that should be exempt from being disabled.
        key (str): Name of private key file to use.
            Defaults to the :setting:`security_key` setting.
        cert (str): Name of certificate file to use.
            Defaults to the :setting:`security_certificate` setting.
        store (str): Directory containing certificates.
            Defaults to the :setting:`security_cert_store` setting.
        digest (str): Digest algorithm used when signing messages.
            Default is ``sha1``.
        serializer (str): Serializer used to encode messages after
            they've been signed.  See :setting:`task_serializer` for
            the serializers supported.  Default is ``json``.
    """
    from celery.security import setup_security

    return setup_security(
        allowed_serializers, key, cert, store, digest, serializer, app=self
    )


# Traceback (kombu.exceptions.ContentDisallowed)
[2018-09-10 02:33:07,446: CRITICAL/MainProcess] Unrecoverable error: ContentDisallowed('Refusing to deserialize disabled content of type json (application/json)',)
Traceback (most recent call last):
File "/usr/lib/python3.6/site-packages/celery/worker/worker.py", line 205, in start
self.blueprint.start(self)
File "/usr/lib/python3.6/site-packages/celery/bootsteps.py", line 119, in start
step.start(parent)
File "/usr/lib/python3.6/site-packages/celery/bootsteps.py", line 369, in start
return self.obj.start()
File "/usr/lib/python3.6/site-packages/celery/worker/consumer/consumer.py", line 317, in start
blueprint.start(self)
File "/usr/lib/python3.6/site-packages/celery/bootsteps.py", line 119, in start
step.start(parent)
File "/usr/lib/python3.6/site-packages/celery/worker/consumer/consumer.py", line 593, in start
c.loop(*c.loop_args())
File "/usr/lib/python3.6/site-packages/celery/worker/loops.py", line 91, in asynloop
next(loop)
File "/usr/lib/python3.6/site-packages/kombu/asynchronous/hub.py", line 354, in create_loop
cb(*cbargs)
File "/usr/lib/python3.6/site-packages/kombu/transport/redis.py", line 1040, in on_readable
self.cycle.on_readable(fileno)
File "/usr/lib/python3.6/site-packages/kombu/transport/redis.py", line 337, in on_readable
chan.handlers[type]()
File "/usr/lib/python3.6/site-packages/kombu/transport/redis.py", line 667, in _receive
ret.append(self._receive_one(c))
File "/usr/lib/python3.6/site-packages/kombu/transport/redis.py", line 697, in _receive_one
message, self._fanout_to_queue[exchange])
File "/usr/lib/python3.6/site-packages/kombu/transport/virtual/base.py", line 983, in _deliver
callback(message)
File "/usr/lib/python3.6/site-packages/kombu/transport/virtual/base.py", line 633, in _callback
return callback(message)
File "/usr/lib/python3.6/site-packages/kombu/messaging.py", line 624, in _receive_callback
return on_m(message) if on_m else self.receive(decoded, message)
File "/usr/lib/python3.6/site-packages/celery/worker/consumer/gossip.py", line 201, in on_message
_, event = prepare(message.payload)
File "/usr/lib/python3.6/site-packages/kombu/message.py", line 207, in payload
return self._decoded_cache if self._decoded_cache else self.decode()
File "/usr/lib/python3.6/site-packages/kombu/message.py", line 192, in decode
self._decoded_cache = self._decode()
File "/usr/lib/python3.6/site-packages/kombu/message.py", line 197, in _decode
self.content_encoding, accept=self.accept)
File "/usr/lib/python3.6/site-packages/kombu/serialization.py", line 256, in loads
raise self._for_untrusted_content(content_type, 'disabled')
kombu.exceptions.ContentDisallowed: Refusing to deserialize disabled content of type json (application/json)

# Fixed code
def setup_security(
    self,
    allowed_serializers=None,
    key=None,
    cert=None,
    store=None,
    digest=DEFAULT_SECURITY_DIGEST,
    serializer="json",
):
    """Setup the message-signing serializer.

    This will affect all application instances (a global operation).

    Disables untrusted serializers and if configured to use the ``auth``
    serializer will register the ``auth`` serializer with the provided
    settings into the Kombu serializer registry.

    Arguments:
        allowed_serializers (Set[str]): List of serializer names, or
            content_types that should be exempt from being disabled.
        key (str): Name of private key file to use.
            Defaults to the :setting:`security_key` setting.
        cert (str): Name of certificate file to use.
            Defaults to the :setting:`security_certificate` setting.
        store (str): Directory containing certificates.
            Defaults to the :setting:`security_cert_store` setting.
        digest (str): Digest algorithm used when signing messages.
            Default is ``sha256``.
        serializer (str): Serializer used to encode messages after
            they've been signed.  See :setting:`task_serializer` for
            the serializers supported.  Default is ``json``.
    """
    from celery.security import setup_security

    return setup_security(
        allowed_serializers, key, cert, store, digest, serializer, app=self
    )