'Prepare the ``connection`` for :meth:`urllib3.util.ssl_wrap_socket`
and establish the tunnel if proxy is used.'

def _prepare_conn(self, conn):

    if isinstance(conn, VerifiedHTTPSConnection):
        conn.set_cert(key_file=self.key_file, cert_file=self.cert_file, cert_reqs=self.cert_reqs, ca_certs=self.ca_certs, assert_hostname=self.assert_hostname, assert_fingerprint=self.assert_fingerprint)
        conn.ssl_version = self.ssl_version
    return conn
