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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 refresh():
 """ Refreshes an existing JWT by creating a new one that is a copy of the old except that it has a refrehsed access expiration. .. example:: $ curl http://localhost:5000/refresh -X GET \ -H "Authorization: Bearer <your_token>" """

    old_token = guard.read_token_from_header()
    new_token = guard.refresh_jwt_token(old_token)
    ret = {'access_token': new_token}
    return flask.jsonify(ret), 200