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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 expires_in(self):
 """ Returns the time until the token expires. :return: The remaining time until expiration in seconds or 0 if the token has expired. """

        time_left = self.expires_at - int(time.time())

        if time_left > 0:
            return time_left
        return 0