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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 _get_jwt_for_audience(self, audience):
 """Get a JWT For a given audience. If there is already an existing, non-expired token in the cache for the audience, that token is used. Otherwise, a new token will be created. Args: audience (str):
 The intended audience. Returns: bytes: The encoded JWT. """

        token, expiry = self._cache.get(audience, (None, None))

        if token is None or expiry < _helpers.utcnow():
            token, expiry = self._make_jwt_for_audience(audience)
            self._cache[audience] = token, expiry

        return token