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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 sync_client(self):
 """Synchronous OAuth 2.0 Bearer client"""

        if not self._sync_client:
            self._sync_client = AlfSyncClient(
                token_endpoint=self.config.get('OAUTH_TOKEN_ENDPOINT'),
                client_id=self.config.get('OAUTH_CLIENT_ID'),
                client_secret=self.config.get('OAUTH_CLIENT_SECRET')
            )
        return self._sync_client