Can Facebook's "Single Sign On" be achieved within a mobile web app?

It's my first posting on here (although I've been using this site for reference for quite some time).

I've been trying for several days now to find or dream up a way to use Facebook's "Single Sign On" from within a mobile web app (not a native iOS or And开发者_如何转开发roid app) to automatically sign a user into a web app if they are already logged into Facebook from the native Facebook app on their mobile device for example.

My limited knowledge is telling me that it can't be done since the mobile browser and the 'system' (iOS for example) are too separated (I can't, I don't think, have my mobile web app use or access the native Facebook app on a mobile device in any way).

I have found and read the iOS, Android AND Mobile documentation provided by Facebook (https://developers.facebook.com/docs/guides/mobile/) which all seems to make enough sense, but after days of trawling through everything else I could find on the subject there doesn't seem to be a way to use, for example, the Facebook app on an iPhone or Android device to automatically log a user in to my web app if he/she is already logged into Facebook.

I've read lots about doing this from within 3rd party native apps and also other people trying to achieve a similar thing from within Desktop apps but I'm trying and hoping to be able to achieve this from a web app running within a mobile web browser.

I'd be very grateful for any help, opinions or pointers in the right direction since I think this would be an excellent step forward in UI for mobile web apps to have (not just the native apps).

Many thanks in advance...

Probably a bit late to the party but in case anyone else is wondering yes it's possible with Cordova/Phonegap and the Facebook Connect Plugin: https://github.com/davejohnson/phonegap-plugin-facebook-connect/

Using the FB.getLoginStatus() method at startup allows to check if the user is already signed in with the native Facebook App and retrieve its profile. More details in the examples provided in the repo.

I have not yet implemented it myself, but seems possible according to:

http://developers.facebook.com/docs/mobile/web/build/#login