'Load a private key and the corresponding certificate. The certfile
string must be the path to a single file in PEM format containing the
certificate as well as any number of CA certificates needed to
establish the certificate\'s authenticity. The keyfile string, if
present, must point to a file containing the private key. Otherwise
the private key will be taken from certfile as well.'

def load_cert_chain(self, certfile, keyfile=None):

    self._certfile = certfile
    self._keyfile = keyfile
