`invalid_grant` failures under Python3

[tseaver]

When running with the branch from googleapis/google-cloud-python#580:

$ .tox/regression3/bin/python regression/run_regression.py --package=storage
ERROR

======================================================================
ERROR: setUpModule (storage)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/tseaver/projects/agendaless/Google/src/gcloud-python/regression/storage.py", line 42, in setUpModule
    SHARED_BUCKETS['test_bucket'] = CONNECTION.create_bucket(bucket_name)
  File "/home/tseaver/projects/agendaless/Google/src/gcloud-python/.tox/regression3/lib/python3.4/site-packages/gcloud/storage/connection.py", line 351, in create_bucket
    data={'name': bucket.name})
  File "/home/tseaver/projects/agendaless/Google/src/gcloud-python/.tox/regression3/lib/python3.4/site-packages/gcloud/storage/connection.py", line 239, in api_request
    method=method, url=url, data=data, content_type=content_type)
  File "/home/tseaver/projects/agendaless/Google/src/gcloud-python/.tox/regression3/lib/python3.4/site-packages/gcloud/storage/connection.py", line 176, in make_request
    body=data)
  File "/home/tseaver/projects/agendaless/Google/src/gcloud-python/.tox/regression3/lib/python3.4/site-packages/oauth2client/util.py", line 135, in positional_wrapper
    return wrapped(*args, **kwargs)
  File "/home/tseaver/projects/agendaless/Google/src/gcloud-python/.tox/regression3/lib/python3.4/site-packages/oauth2client/client.py", line 530, in new_request
    self._refresh(request_orig)
  File "/home/tseaver/projects/agendaless/Google/src/gcloud-python/.tox/regression3/lib/python3.4/site-packages/oauth2client/client.py", line 744, in _refresh
    self._do_refresh_request(http_request)
  File "/home/tseaver/projects/agendaless/Google/src/gcloud-python/.tox/regression3/lib/python3.4/site-packages/oauth2client/client.py", line 807, in _do_refresh_request
    raise AccessTokenRefreshError(error_msg)
oauth2client.client.AccessTokenRefreshError: invalid_grant

----------------------------------------------------------------------

• Those tests use the GOOGLE_APPLICATION_CREDENTIALS envvar, and run fine under Python2.
• All gcloud-python unit tests pass on that branch under Python2 and Python3.

[craigcitro]

cc @anthmgoogle

[dhermes]

It's a formatting issue of bytes vs. string.

In Python2:

>>> body
'assertion=eyJ...'

In Python3:

>>> body
'assertion=b%22b%27eyJ...'

Decoding, this is a bit of a mess:

>>> urllib.unquote('b%22b%27eyJ...')
'b"b\'eyJ...'

---

Python2

>>> urlparse.parse_qs(WORKS)
{'assertion': ['eyJ...REDACTED...Q.eyJ...REDACTED...X0.3L2...REDACTED...Adg'],
 'grant_type': ['urn:ietf:params:oauth:grant-type:jwt-bearer']}

Python3

>>> urlparse.parse_qs(NOT_WORKS)
{'assertion': ['b"b\'eyJ...REDACTED...fQ\'.b\'eyJ...REDACTED...In0\'".v4M...REDACTED...g0'],
 'grant_type': ['urn:ietf:params:oauth:grant-type:jwt-bearer']}

[dhermes]

@craigcitro Can you assign this issue to me? I am working on it.

[craigcitro]

@dhermes it won't let me assign to anyone outside our org, unfortunately.