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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:
 async def start_authentication(self):
 """Start the authentication process. This method will show the expected PIN on screen. """

        _, code = await self.http.post_data(
            'pair-pin-start', headers=_AIRPLAY_HEADERS)
        if code != 200:
            raise DeviceAuthenticationError('pair start failed')