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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 fetch_token(self):
 """Gains token from secure backend service. :return: Token formatted for Cocaine protocol header. """

        grant_type = 'client_credentials'

        channel = yield self._tvm.ticket_full(
            self._client_id, self._client_secret, grant_type, {})
        ticket = yield channel.rx.get()

        raise gen.Return(self._make_token(ticket))