code: def _validate_apns_certificate(self, certfile):
  		
  
  		try:
  			with open(certfile, "r") as f:
  				content = f.read()
  				check_apns_certificate(content)
  		except Exception as e:
  			raise ImproperlyConfigured(
  				"The APNS certificate file at %r is not readable: %s" % (certfile, e)
  			)
docs: Validate the APNS certificate at startup.