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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def blacklist_token():
 """ Blacklists an existing JWT by registering its jti claim in the blacklist. .. example:: $ curl http://localhost:5000/blacklist_token -X POST \ -d '{"token":"<your_token>"}' """

    req = flask.request.get_json(force=True)
    data = guard.extract_jwt_token(req['token'])
    blacklist.add(data['jti'])
    return flask.jsonify(message='token blacklisted ({})'.format(req['token']))