Recognising registered user (from another site)

[Seymour Clufley]

Yo all,

Having returned from holiday I'm curious about something Facebook have started doing, and would like to implement a similar service on my own website. It's an HTML/server question and, though I've asked it on a more suitable forum, I think somebody here may know the answer.

If you're a registered user of Facebook, you can comment on something on another website using your FB identity. Your FB identity seems to be automatically recognised; the FB commenting stuff appears without you doing anything. If you post a comment, it gets added to that site AND to your Facebook wall.

I don't understand how they do this. How do they know it's you looking at this other website? Is it done by your IP address or the new client-side storage thing?

I ask because I'd like to do something similar for my own site - ie allowing registered users of my site to comment on things on other websites.

Thanks for reading,
Seymour.

[IdeasVacuum]

How do they know it's you looking at this other website?

If you are using the PC that you used to register with FB, then may be they saved a cookie on your system for this purpose?

[naw]

I'm guessing that (as IdeasVacuum said) it is a cookie entry in your browsers cookie file that identifies you, but since cookies are supposed to be readable only from the domain that created it, I guess the form that allows you to create the post actually executes from the FB site and is embedded in your website's pages.

[TomS]

All Facebook boxes on other sites are in fact embedded via iframe.

[Seymour Clufley]

Ah! An iFrame... of course!