How to use the taskcluster.utils.dumpJson function in taskcluster

def _makeHttpRequest(self, method, route, payload):
        """ Make an HTTP Request for the API endpoint.  This method wraps
        the logic about doing failure retry and passes off the actual work
        of doing an HTTP request to another method."""

        url = self._constructUrl(route)
        log.debug('Full URL used is: %s', url)

        hawkExt = self.makeHawkExt()

        # Serialize payload if given
        if payload is not None:
            payload = utils.dumpJson(payload)

        # Do a loop of retries
        retry = -1  # we plus first in the loop, and attempt 1 is retry 0
        retries = self.options['maxRetries']
        while retry < retries:
            retry += 1
            # if this isn't the first retry then we sleep
            if retry > 0:
                time.sleep(utils.calculateSleepTime(retry))
            # Construct header
            if self._hasCredentials():
                sender = mohawk.Sender(
                    credentials={
                        'id': self.options['credentials']['clientId'],
                        'key': self.options['credentials']['accessToken'],
                        'algorithm': 'sha256',

] + scopes)
    sigStr = '\n'.join(sig).encode()

    if isinstance(accessToken, six.text_type):
        accessToken = accessToken.encode()
    sig = hmac.new(accessToken, sigStr, hashlib.sha256).digest()

    cert['signature'] = utils.encodeStringForB64Header(sig)

    newToken = hmac.new(accessToken, cert['seed'], hashlib.sha256).digest()
    newToken = utils.makeB64UrlSafe(utils.encodeStringForB64Header(newToken)).replace(b'=', b'')

    return {
        'clientId': name or clientId,
        'accessToken': newToken,
        'certificate': utils.dumpJson(cert),
    }