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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_certs(request, certs_url):
 """Fetches certificates. Google-style cerificate endpoints return JSON in the format of ``{'key id': 'x509 certificate'}``. Args: request (google.auth.transport.Request):
 The object used to make HTTP requests. certs_url (str):
 The certificate endpoint URL. Returns: Mapping[str, str]: A mapping of public key ID to x.509 certificate data. """

    response = request(certs_url, method='GET')

    if response.status != http_client.OK:
        raise exceptions.TransportError(
            'Could not fetch certificates at {}'.format(certs_url))

    return json.loads(response.data.decode('utf-8'))