Invalid JWT Token when using Service Account JSON

OS type and version

macOS Sierra running a Debian Jessie Docker Container

Python version and virtual environment information python --version

CPython 3.5.0, no virtual environment

google-cloud-python version pip show google-cloud, pip show google-<service> or pip freeze

google-cloud-bigquery==0.23.0

Stacktrace if available

Traceback (most recent call last):
  File "/usr/local/lib/python3.5/code.py", line 91, in runcode
    exec(code, self.locals)
  File "<console>", line 1, in <module>
  File "/usr/local/lib/python3.5/site-packages/celery/local.py", line 191, in __call__
    return self._get_current_object()(*a, **kw)
  File "/app/warehouse/celery.py", line 53, in __call__
    return super().__call__(pyramid_env["request"], *args, **kwargs)
  File "/usr/local/lib/python3.5/site-packages/celery/app/task.py", line 379, in __call__
    return self.run(*args, **kwargs)
  File "/app/warehouse/packaging/tasks.py", line 58, in compute_trending
    query.run()
  File "/usr/local/lib/python3.5/site-packages/google/cloud/bigquery/query.py", line 364, in run
    method='POST', path=path, data=self._build_resource())
  File "/usr/local/lib/python3.5/site-packages/google/cloud/_http.py", line 299, in api_request
    headers=headers, target_object=_target_object)
  File "/usr/local/lib/python3.5/site-packages/google/cloud/_http.py", line 193, in _make_request
    return self._do_request(method, url, headers, data, target_object)
  File "/usr/local/lib/python3.5/site-packages/google/cloud/_http.py", line 223, in _do_request
    body=data)
  File "/usr/local/lib/python3.5/site-packages/google_auth_httplib2.py", line 187, in request
    self._request, method, uri, request_headers)
  File "/usr/local/lib/python3.5/site-packages/google/auth/credentials.py", line 116, in before_request
    self.refresh(request)
  File "/usr/local/lib/python3.5/site-packages/google/oauth2/service_account.py", line 318, in refresh
    request, self._token_uri, assertion)
  File "/usr/local/lib/python3.5/site-packages/google/oauth2/_client.py", line 143, in jwt_grant
    response_data = _token_endpoint_request(request, token_uri, body)
  File "/usr/local/lib/python3.5/site-packages/google/oauth2/_client.py", line 109, in _token_endpoint_request
    _handle_error_response(response_body)
  File "/usr/local/lib/python3.5/site-packages/google/oauth2/_client.py", line 59, in _handle_error_response
    error_details, response_body)
google.auth.exceptions.RefreshError: ('invalid_grant: Invalid JWT Signature.', '{\n  "error" : "invalid_grant",\n  "error_description" : "Invalid JWT Signature."\n}')

Steps to reproduce

Try to query anything in BigQuery using a service account with "Viewer" permissions and GOOGLE_APPLICATION_CREDENTIALS pointed to a JSON file downloaded when creating the service account.

Code example

bq = bigquery.Client()
query = bq.run_sync_query(
        """ SELECT project,
                   IF(
                        STDDEV(downloads) > 0,
                        (todays_downloads - AVG(downloads))/STDDEV(downloads),
                        NULL
                    ) as zscore
            FROM (
                SELECT project,
                       date,
                       downloads,
                       FIRST_VALUE(downloads) OVER (
                            PARTITION BY project
                            ORDER BY DATE DESC
                            ROWS BETWEEN UNBOUNDED PRECEDING
                                AND UNBOUNDED FOLLOWING
                        ) as todays_downloads
                FROM (
                    SELECT file.project as project,
                           DATE(timestamp) AS date,
                           COUNT(*) as downloads
                    FROM `the-psf.pypi.downloads*`
                    WHERE _TABLE_SUFFIX BETWEEN
                        FORMAT_DATE(
                            "%Y%m%d",
                            DATE_ADD(CURRENT_DATE(), INTERVAL -31 day))
                        AND
                        FORMAT_DATE(
                            "%Y%m%d",
                            DATE_ADD(CURRENT_DATE(), INTERVAL -1 day))
                    GROUP BY file.project, date
                )
            )
            GROUP BY project, todays_downloads
            HAVING SUM(downloads) >= 5000
            ORDER BY zscore DESC
        """
    )
query.use_legacy_sql = False
query.run()