CODEWITHSUNDEEP
facebookauthentication
Joe Völker
Joe Völker

Reputation: 791

Dertermine if user is logged in to Facebook w/o using Facebook api

I'm serving a list of events to my clients’ website. They include it via php/curl (rather than iFrame), so they can fully customize the CSS.

However, this means that I can’t use the Facebook API to find out wether a visitor of my client’s page is logged in to FB: The FB-API call needs to be signed by an application and shall only be called from the domain the application is associated with. (That would be my server’s domain, but the requests are coming from my client’s page.)

Back in the old days, accessing a user profile on FB would issue a 404 error, if not logged in. 

<script type="text/javascript" src="https://www.facebook.com/pianojoe" onload="enable_social_links()" onerror="not_logged_in_to_facebook()" async="async"></script>

That was convenient, but FB took care :-/ of it.

I want to show FB-links for the events in my calendar only if the page visitor is logged in to Facebook.

My question: How do I find out if a page visitor is logged in to Facebook if I can’t determine the domain of the referring page beforehand, and therefore not use the Facebook API?

Upvotes: 0

Views: 1476

Answers (1)

C3roe
C3roe

Reputation: 96407

The Facebook PHP SDK has a (relatively new) method called getLoginStatusUrl.

It creates a simple URL that you redirect the user’s browser to, which takes them to Facebook, where his login status is checked, and then redirects them back to one of three different URLs of your app, that you can specify.

ok_session is the one that you would be mainly interested in here: “URL to return if the user is logged in to Facebook.”

(The other two are no_user for when the user is logged out of Facebook, and no_session for when Facebook themselves can’t figure out the user’s status, because there’s no user-specific FB cookies whatsoever set in their browser.)

So you could set ok_session to an URL of your application with an additional GET parameter like ?logged_into_fb=true (the other two options, if not specified explicitly, will then only redirect back to your app’s base URL) – and that way, when the user is redirected back to your app with that parameter, you know they are currently logged into Facebook.

Whether or not you are actually using the FB PHP SDK does not really matter – by looking at the source code of the method it’s relatively easy to figure out how the actual URL is build, so you could easily adapt that and use it without the SDK as well.

Upvotes: 1

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