def _decode_exp(self, access_token=None):
c = self.get_credentials()<EOL>jwt = access_token or c.access_token<EOL>x = self.decode_jwt_payload(jwt)<EOL>if '<STR_LIT>' in x:<EOL><INDENT>try:<EOL><INDENT>exp = int(x['<STR_LIT>'])<EOL><DEDENT>except ValueError:<EOL><INDENT>raise PanCloudError(<EOL>"<STR_LIT>")<EOL><DEDENT>else:<EOL><INDENT>self.jwt_exp = exp<EOL>return exp<EOL><DEDENT><DEDENT>else:<EOL><INDENT>raise PanCloudError("<STR_LIT>")<EOL><DEDENT>
Extract exp field from access token.

        Args:
            access_token (str): Access token to decode. Defaults to ``None``.

        Returns:
            int: JWT expiration in epoch seconds.