Recognize a website user without logging in?

Question

I would like to create a piece of code that can be embedded on different sites (widget).

Is there a way my code can identify a user without logging in? Ie, can I use any of the established authentication mechanisms that float across the network to reliably identify them through instances of this widget?

I do not need (and I can not) use any information about this user, just identify them.

Websites will be heterogeneous; there is no guarantee that they will have any common aspects, so the widget code must be completely autonomous.

Answer 1

, , cookie. , cookie.

Electronic Frontier Foundation . , :

• User-Agent
• http-accept
• cookie .

, , , , , .

Answer 2

OpenID - SSO , OpenID. , .

Answer 3

, Sign Sign In. , , , . Wich . - SSO. Ff , .

. javascript-, Google? javascript , , iframe.

src ( ). <img src=contentserver.com/track.php?id=12345668>

script (track.php ), , .

.

Edit2

javascript. javascript . , . javascript unique_id(), . track.php ajax, , .

Answer 4

Open-ID, - , , , :

cookie , , URL-

, foo.com :

http://bar.com/addwidget1?backtoo=http://foo.com/main/

bar.com cookie, :

foo.com/user-id/

• .
• , .
• - .
• cookie.

• , .

Answer 5

OpenID . , , , cookie, URL.

OpenID, - . , , , OpenID, . , , OpenID, cookie .

Facebook ; Facebook ( , ) - .