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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 is_authenticated(self):
 """Tests if an agent is authenticated to this session. return: (boolean) - true if valid authentication credentials exist, false otherwise compliance: mandatory - This method must be implemented. """

        if self._proxy is None:
            return False
        elif self._proxy.has_authentication():
            return self._proxy.get_authentication().is_valid()
        else:
            return False