The quick version: I’ve found a way to abuse the login mechanism for both Twitter and Google to detect whether a user is logged in to that service. Facebook provides an API for this. So I provide a cross-browser javascript template that works for all 3 networks. If you want to get straight to the code jump to the implementation section or check out the Social Network Login Status Detector Demo.
Introduction
I was interested in seeing whether it would be possible to track which social networks a website visitor is logged into at the time of their visit; it could be cool for selecting which social media buttons you show them, what sort of marketing you do to them, or simply to evaluate whether you should be participating more on a certain social network. I was interested in Facebook, Twitter and Google+; as an SEO I was also interested in whether people were logged into a general Google account so I could compare which percentage of those had a Google+ account.
A quick search turned up an interesting post from Mike Cardwell who had a method for doing this for Facebook, Twitter and Gmail, but unfortunately it didn’t work in Internet Explorer. Secondly, I knew there was a better method than Mike’s for Facebook, which I’d seen presented by Mat Clayton of Mixcloud; he uses Facebook’s API to do the same thing (see slide 15). Mat’s method works great across browsers, so that solved the Facebook side of this.
Finding a way in to Twitter and Google+
Wat I needed was a method for detecting whether a visitor to my site was logged in to Twitter, Google and more specifically Google+.
Thanks to abraham from Hacker News I discovered that Twitter has an undocumented endpoint that simply returns true or false for whether the current user is logged in! It is very simple:
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<script>
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function twitterLoginStatus(state) {
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alert(state);
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}
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</script>
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<script src='https://api.twitter.com/sessions/present.js?callback=twitterLoginStatus'></script>
However, due to boring technical details concerning MIME types this code doesn’t work on IE9, which (unfortunately) for many purposes makes it less than ideal.
Browsers nowadays are very sensitive to cross site requests and the all to common exploits that abuse them, and so unless the 3rd party site plans to allow it using javascript for this is probably going to be difficult. The other great way to make cross domain requests is with image tags.
Tricking login mechanisms
I came up with the theory that I needed to try to access and image on Twitter/Google’s sites that would only be available to users when they are logged in. Using javascript I could detect whether the image loaded or not and thus determine whether the user was loggedin. However, these are obviously going to be few and far between (image assets are often static and so on CDNs and/or not protected in such a manner), if they exist at all (I didn’t find any), so I was back to square one. I needed a protected area of the site, but needed the file contents to be an image.
My winning moment was realising that some naive login systems might be open to abuse for exactly this purpose. It is often the case that you try to access a specific page on a site, lets say the “Upload a photo” page but you need to be logged in to do so. If you are not logged into the site in question, when you visit the URL the page redirects to the Login page to authenticate you are who you say you are; however the site wants to be helpful and send you to the page you were looking for so they keep a track of that target page in the URL as a parameter and then helpfully redirect you to that page after login is complete.
What happens if you visit the login page with a ‘redirect on login’ parameter and you are already logged in? When implemented in a naive fashion you are simply immediately redirected to the page specified in the parameter. Some sites limit that parameter to being another page on the same domain, but we’ll see that doesn’t help for this trick.
This mechanism is open to abuse in exactly the way I needed; I could set the ‘redirect on login’ page to be an image file on the same domain. For example:
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<img src="https://twitter.com/login?redirect_after_login=%2Fimages%2Fspinner.gif" />
In this example, if I am logged in Twitter is kind enough to 302 redirect me to the image file I specified, but if I am not logged in I am show the login page. It turns out that both Twitter and Google’s login mechanisms are susceptible to exactly this trick. It seems LinkedIn and Tumblr are currently immune to this, though I didn’t dig too deep so there might be another redirect URL for them.
Putting it all together
From this point on it was quite easy to hack together some javascript; just stick this code in the <head></head> section of your page:
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<script type="text/javascript">
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function show_login_status(network, status)
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{
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if (status)
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{
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alert("Logged in to " + network);
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}else{
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alert("Not logged in to " + network);
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}
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}
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</script>
Then, anywhere in your code that seems like a nice place stick this HTML:
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<img style="display:none;"
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onload="show_login_status('Google', true)"
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onerror="show_login_status('Google', false)"
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src="https://accounts.google.com/CheckCookie?continue=https%3A%2F%2Fwww.google.com%2Fintl%2Fen%2Fimages%2Flogos%2Faccounts_logo.png&followup=https%3A%2F%2Fwww.google.com%2Fintl%2Fen%2Fimages%2Flogos%2Faccounts_logo.png&chtml=LoginDoneHtml&checkedDomains=youtube&checkConnection=youtube%3A291%3A1"
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/>
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<img style="display:none;"
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onload="show_login_status('GooglePlus', true)"
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onerror="show_login_status('GooglePlus', false)"
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src="https://plus.google.com/up/?continue=https://www.google.com/intl/en/images/logos/accounts_logo.png&type=st&gpsrc=ogpy0"
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/>
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<img style="display:none;" src="https://twitter.com/login?redirect_after_login=%2Fimages%2Fspinner.gif" onload="show_login_status('Twitter', true)" onerror="show_login_status('Twitter', false)" />
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<div id="fb-root"></div>
Finally, somewhere after that HTML stick this Javascript:
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<script>
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window.fbAsyncInit = function(){
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FB.init({ appId:'xxxxxxxxxxxx', status:true, cookie:true, xfbml:true});
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FB.getLoginStatus(function(response){
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if (response.status != "unknown")
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{
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show_login_status("Facebook", true);
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}else{
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show_login_status("Facebook", false);
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}
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});
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};
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// Load the SDK Asynchronously
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(function(d){
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var js, id = 'facebook-jssdk'; if (d.getElementById(id)) {return;}
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js = d.createElement('script'); js.id = id; js.async = true;
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js.src = "//connect.facebook.net/en_US/all.js";
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d.getElementsByTagName('head')[0].appendChild(js);
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}(document));
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</script>
You will need to replace xxxxxxxxx above with the appID for an app created for your domain; if you don’t have one you can create one in about 60 seconds. Simply visit https://developers.facebook.com/apps whilst logged in to Facebook, and click “Create New App”. You will be prompted for a “Display Name”, and you can enter any old dummy text here and press Continue. On the next page it is only necessary to fill out the “App Domain” and the “Website” with the URL of the domain you want to use this code on. Do that, save changes and grab the “App ID” from the top of the page and enter it in the code above.
You should be all set! Now you can change your alert() functions to do whatever you want based on the login status of the user. See a demo of it in action Social Network Login Status Detector Demo.
Wrap up
In my testing this worked on a range of versions of Firefox and Chrome, IE versions 7 and up, Safari and Opera. It may be that these loopholes get fixed, but in the meantime I implore you to only use this in nice ways. There is an argument that a 3rd party even knowing what other sites you are logged into is a breach of your privacy, and I can certainly see why some people would feel like that (especially if this was scaled up to more personal sites that you might be logged into). If you want to prevent this then for Firefox you can try RequestPolicy or NoScript. For Chrome you can give ScriptNo a shot. On IE you can try giving Firefox or Chrome a try. 😉
However, I do also think that this sort of thing can be used in good ways – serving only a subset of social buttons to your users, or determining whether you should be providing support on a given social platform etc. If anyone has any nice suggestions for other ways you could use (nicely) use this, I’d love to hear.
This was just the bit of code I was looking for to fix a google docs glitch. Thanks!
http://www.joshualawrencechamberlain.com/autobiography.php
Very interesting approach to this challenge. I have been trying to think of a way to detect whether someone is logged into a social network or other service, but wasn’t able to figure it out. Looks like you’ve solved this, at least temporarily, until they change something so that this no longer works.
I try to detect visitators from social netkworm from year but useles! Now after I read this article I will try to follow your advices and I hope to work!
Thanks for this great article!
Really nice. I setted it up and worked fine. It still works fine in Twitter em G+. With Facebook I have an error message saying the SDK version is not supported anymore! Any idea how to fix? Anyway, thank you so much!
your twitter demo doesn’t work for me :/
Tom, you really over did it here, thanks for this update, going to add this in my meme website. thanks once more.
I am a beginner at this, but is it possible to indentify the accounts who are logged in? it is possible to know if somone is logged in in a social media site, but is it possible to know the name/adress of that account? If that is possible than clearing cookies is useless because they will track you anyway everytime you are logged in.
very cool!
is there a way to detect Pinterest login status?
Love it!
Is it possible to detect their username or avatar?
This is smart but rather bordering on the privacy issues.
Anyone got any ideas to put it to good use ?
your twitter demo doesn’t work anymore for me either :/
Hi Tom
The Twitter demo doesn’t seem to be working anymore. Do you have any ideas on how to fix this?
Hi Tom,
is there a way to check whether the user is logged in a social network and if yes, show their profile picture and name somewehere on the website?
Thanks, Roman
The proof of concept failed to recognize that I was currently logged in to Twitter.
Nice solution to a dilemma we have had for some time now. It’s all nice to send your user to a G+ service but it get’s very nice when you can add logic according to their login/off status. Thanks!
very good
Hello, would you like to post this on GitHub, I would like to help maintain and add some improvements.
I would like to help maintain in github
Nice post. Is there anyway we can get the username for each as well. For e.g. if a user is logged on to gmail, fb or twitter then display the associated username or email related to the account?
Excelente 😀 Too powerfull in evil hands xD
how can detect name and family
please help me i need that code
Hi, Does the twitter method still work? I can’t get anything from it ATM and wondered if twitter have broken this method?
Thanks for sharing this. This was a big help in some social media research we conducted on MDN. I wrote a follow-up blog post with an updated Twitter example for anyone interested.
Sir,May i know the email id of visitor who is currently logged in.
Nice site! Do you know some linked in things too?
Sir is there any way to know the email id of visitor who is currently logged in.