Cover possibility of redirects to other origins within the popin

[krgovind]

In privacycg/storage-partitioning/issues/28, @darkowic mentioned a use-case that involves a redirect/OIDC exchange with another SSO provider within the popin. Is that a scenario we can support with this proposal (assuming that state is still partitioned to the opener)?

[arichiv]

redirects within the popin are no issue, but the popin itself remains partitioned regardless of redirect/navigation destination and headers permitting the popin context are required of all pages loaded.

[krgovind]

redirects within the popin are no issue, but the popin itself remains partitioned regardless of redirect/navigation destination and headers permitting the popin context are required of all pages loaded.

That makes sense. Any chance we can document this requirement/behavior in the explainer? I didn't spot it on a quick skim, apologies if it's already there!

[arichiv]

It's kind of addressed, but I could add more details:

Navigating to or redirecting through a page without a Popin-Policy that permits the opening context to do so will cause the popin to automatically close and report the error to the opening context.