Trouble with oauth2client.client.Storage

[Fabrizio Farinacci]

I'm trying to use OAuth2 with my App Engine application, but I keep getting the following error:

Encountered unexpected error from ProtoRPC method implementation: IOError ([Errno 30] Read-only file system: 'credentials.dat')
Traceback (most recent call last):
  File "/base/data/home/runtimes/python27/python27_lib/versions/third_party/protorpc-1.0/protorpc/wsgi/service.py", line 181, in protorpc_service_app
    response = method(instance, request)
  File "/base/data/home/runtimes/python27/python27_lib/versions/third_party/endpoints-1.0/endpoints/api_config.py", line 1332, in invoke_remote
    return remote_method(service_instance, request)
  File "/base/data/home/runtimes/python27/python27_lib/versions/third_party/protorpc-1.0/protorpc/remote.py", line 412, in invoke_remote_method
    response = method(service_instance, request)
  File "/base/data/home/apps/s~art-everywhere/7.385356767964097452/main.py", line 438, in upload_putphoto
    gd_client = PicasaWA.login()
  File "/base/data/home/apps/s~art-everywhere/7.385356767964097452/main.py", line 1653, in login
    storage.put(credentials)
  File "/base/data/home/apps/s~art-everywhere/7.385356767964097452/oauth2client/client.py", line 325, in put
    self.locked_put(credentials)
  File "/base/data/home/apps/s~art-everywhere/7.385356767964097452/oauth2client/file.py", line 113, in locked_put
    f = open(self._filename, 'wb')
IOError: [Errno 30] Read-only file system: 'credentials.dat'

It looks like there's a problem with the write used in the library.

Here's a snippet of the code I used:

def login(cls):
    scope = 'https://picasaweb.google.com/data/'
    user_agent = 'picasawebuploader'
    # credential_store = os.path.join(os.path.split(__file__)[0], "credentials.dat")

    storage = Storage("credentials.dat")
    # storage = Storage(credential_store)
    credentials = storage.get()

    # user = users.get_current_user()
    # storage = StorageByKeyName(CredentialsModel, user.user_id(), 'credentials')
    # credentials = storage.get()

    if credentials is None or credentials.invalid:
        flow = flow_from_clientsecrets("client_secrets.json", scope=scope, redirect_uri='urn:ietf:wg:oauth:2.0:oob')
        uri = flow.step1_get_authorize_url()
        logging.info("uri: %s", uri)
        webbrowser.open(uri)
        code = "Here I posted the code retrived by the autentication"
        credentials = flow.step2_exchange(code)
        storage.put(credentials)

    if (credentials.token_expiry - datetime.utcnow()) < timedelta(minutes=5):
        http = httplib2.Http()
        http = credentials.authorize(http)
        credentials.refresh(http)

    gd_client = gdata.photos.service.PhotosService(source=user_agent,
                                                   email=USERNAME,
                                                   additional_headers={'Authorization' : 'Bearer %s' % credentials.access_token})

    return gd_client

What am I doing wrong? Thanks everyone for the help!