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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_authorization_headers(self, context):
 """Gets the authorization headers for a request. Returns: Sequence[Tuple[str, str]]: A list of request headers (key, value) to add to the request. """

        headers = {}
        self._credentials.before_request(
            self._request,
            context.method_name,
            context.service_url,
            headers)

        return list(six.iteritems(headers))