code: def validate_signed_by(message, signer, **config):
      
  
      config = copy.deepcopy(config)
      config['routing_nitpicky'] = True
      config['routing_policy'] = {message['topic']: [signer]}
      return validate(message, **config)
docs: Validate that a message was signed by a particular certificate.
  
      This works much like ``validate(...)``, but additionally accepts a
      ``signer`` argument.  It will reject a message for any of the regular
      circumstances, but will also reject it if its not signed by a cert with the
      argued name.