This CSRF cookie needs to be included on the request to the callback endpoint triggered by the redirect from the OIDC upstream provider. This is not allowed by `Same-Site=Strict` but is allowed by `Same-Site=Lax` because it is a "cross-site top-level navigation" [1].
We didn't catch this earlier with our Dex-based tests because the upstream and downstream issuers were on the same parent domain `*.svc.cluster.local` so the cookie was allowed even with `Strict` mode.
[1]: https://tools.ietf.org/html/draft-ietf-httpbis-cookie-same-site-00#section-3.2
Signed-off-by: Matt Moyer <moyerm@vmware.com>
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