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.
