This is a workaround a behavior change in Chromium v97.
The following text was sent to the blink-dev mailing list:
> This change broke a SingleSignOn login on the FOSS software Discourse. We have a flow like:
>
> 1. User visits forum.siteA.com, click login
> 2. Gets redirected to idp.siteB.com
> 3. Fills login details
> 4. Gets redirected to forum.siteA.com/session/sso_login?parameters
> 5. Gets redirected to forum.siteA.com/homepage
>
> On step 4, the response includes a `set-cookie` header, with proper `HttpOnly; SameSite=Lax; Secure `and set. But if there is an active service worker, the login will fail as that cookie will be rejected by Chromium due to SameSite rules now.
>
> t=2971 [st=258] COOKIE_INCLUSION_STATUS
> --> domain = "forum.siteA.com"
> --> name = "_t"
> --> operation = "store"
> --> path = "/"
> --> status = "EXCLUDE_SAMESITE_LAX, DO_NOT_WARN"
>
> The service worker is a vanilla WorkboxJS service worker that intercepts all GETs with the "Network First" strategy.
>
> Disabling the service worker or using Firefox results in a successful login. There is no warning in either DevTools network tab nor the console that the cookie was rejected.
>
> Chrome 96: login works
> Chrome 97: login does not work
> Chrome 98: login does not work
>
> Is this expected behavior? Even if the request `GET forum.siteA.com` was initiated because of a redirect from a different domain, is it expected that Chrome will silently drop same site cookies from forum.siteA.com?
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