'Create a context factory using this L{PrivateCertificate}\'s certificate
and private key.
@param authorities: A list of L{Certificate} object
@return: A context factory.
@rtype: L{CertificateOptions <twisted.internet.ssl.CertificateOptions>}'

def options(self, *authorities):

    options = dict(privateKey=self.privateKey.original, certificate=self.original)
    if authorities:
        options.update(dict(trustRoot=OpenSSLCertificateAuthorities([auth.original for auth in authorities])))
    return OpenSSLCertificateOptions(**options)
