When Nebula isn't accessed for a while, the Zype access token stored on
the Nebula backend expires. It is then no longer returned by the user
endpoint.
The Nebula frontend has the same issue and keeps polling for the Zype
token in this case.
This isn't implemented in this extractor yet, but at least a specific
error message now prints some helpful advice.
When the 'sessionid' cookie is submitted to the `/auth/login/` endpoint,
the response is always a 403. This typically happens when youtube_dl is
run with both `--netrc` and `--cookies` as your default configuration.
In that situation, the first authentication succeeds and stores the
`sessionid` cookie in the cookie jar. During subsequent authentication
attempts, the cookie is sent alongside and causes the authentication to
fail.
This is very unexpected and we therefore specifically handle this case.
