Identifying Returning Users

Full Title or Meme

Exploring the ways that a web site (aka a relying Party can determine if the current user of the site is known to that site from previous visits.

Single Sign-On to multiple websites is a great improvement in any User Experience it was enabled by the use of Third Party Cookies.
With the demise of Third Party Cookies, new methods for identifying returning users is more complex for a Relying Party.