title: Can Facebook's "Single Sign On" be achieved within a mobile web app?
body: <p>It's my first posting on here (although I've been using this site for reference for quite some time).</p>
  
  <p>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 Android 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.</p>
  
  <p>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).</p>
  
  <p>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.</p>
  
  <p>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.</p>
  
  <p>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).</p>
  
  <p>Many thanks in advance...</p>