According to the "Single sign-on" page on Wikipedia:

A simple version of single sign-on can be achieved over IP networks using cookies but only if the sites share a common DNS parent domain.

This means that if the user has authenticated on login.foo.org, then the web-server on login.foo.org issues an authentication cookie for foo.org domain and the user is able to authenticate on sites like billing.foo.org or wiki.foo.org using that cookie. However, could the login.foo.org make a request to login.bar.org after a successful authentication and thus the user would get two authentication cookies: first-party cookie for foo.org domain and third-party cookie for bar.org domain?

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    This seems like it would work, if the user's browser allows third-party cookies. Bear in mind that Firefox and Safari now block third-party cookies by default, and Chrome has plans to do so as well. See theverge.com/2021/6/24/22547339/….
    – mti2935
    Commented Sep 24, 2021 at 14:26
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    IMO, from the server standpoint it's still possible to do that, but from the Browser side - it's old news. If you check out the date of that quote you can see it's from the good old 2007 Commented Sep 24, 2021 at 15:53

1 Answer 1


The quote you referenced is apparently from the year 2007 and the Browser developer opinion was completely different on Cookies back in the day. As the User @mti2935 pointed out before me 3rd-Party-Cookies are mostly blocked by browsers nowadays.

Nowadays, we are talking about abolishing cookies, thanks to the talks started by Google.

The OAuth 2.0 protocol highly likely offers what you need for SSO authorization nowadays.

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