How is OpenID implemented?

Question

How would you design and implement OpenID components?

(Was \"How does OpenId work\")

I realize this question is somewhat of a duplicate, and yes

Answer 1

Also related:

The super-famous talk by Dick Hardt on Identity 2.0, I suppose almost everyone has watched it, but if you haven't it is a must see.

It is more about the reasoning of the need of things like Open ID and not necessarily about their implementation, though.