<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def validate(self, message):
 """ Validate the message before the consumer processes it. This needs to raise an exception, caught by moksha. Args: message (dict):
 The message as a dictionary. This must, at a minimum, contain the 'topic' key with a unicode string value and 'body' key with a dictionary value. However, the message might also be an object with a ``__json__`` method that returns a dict with a 'body' key that can be a unicode string that is JSON-encoded. Raises: RuntimeWarning: If the message is not valid. UnicodeDecodeError: If the message body is not unicode or UTF-8 and also happens to contain invalid UTF-8 binary. """

        if hasattr(message, '__json__'):
            message = message.__json__()
            if isinstance(message['body'], six.text_type):
                message['body'] = json.loads(message['body'])
            elif isinstance(message['body'], six.binary_type):
                # Try to decode the message body as UTF-8 since it's very likely
                # that that was the encoding used. This API should eventually only
                # accept unicode strings inside messages. If a UnicodeDecodeError
                # happens, let that bubble up.
                warnings.warn('Message body is not unicode', DeprecationWarning)
                message['body'] = json.loads(message['body'].decode('utf-8'))

        # Massage STOMP messages into a more compatible format.
        if 'topic' not in message['body']:
            message['body'] = {
                'topic': message.get('topic'),
                'msg': message['body'],
            }

        # If we're not validating, then everything is valid.
        # If this is turned on globally, our child class can override it.
        if not self.validate_signatures:
            return

        # We assume these match inside fedmsg.crypto, so we should enforce it.
        if not message['topic'] == message['body']['topic']:
            raise RuntimeWarning("Topic envelope mismatch.")

        if not fedmsg.crypto.validate(message['body'], **self.hub.config):
            raise RuntimeWarning("Failed to authn message.")