I'm a bit confused about the difference between a facebook canvas application and a facebook mobile web application. Here is the context of my confusion..
I have a canvas application, let us call its namespace as myfbapp, and I basically can access it from https://apps.facebook.com/myfbapp and after I login to FB it opens up with in Facebook. I'm using java (apache / tomcat) for my server side implementation and for simplicity sake let us say I just have an index.html and a authenticationfilter.java (which implements Filter) in my web application. I don't have any Facebook specific Javascript API (no FB.init() javascript or anything like that ) or code in my index.html. Whenever user accesses my canvas application I first get a request to my web application where I get the signed_request , oauth_token , FB user ID etc which I can use for my internal authentication, session creation etc. I have absolutely no issues with this canvas application and every thing works fine. Please note that when user accesses this app the request I get from the browser to my app server has the signed_request , user_id etc.
Now I wanted to make this app available on mobile devices as well and I thought, oh well all I need to do is add the mobile URL for this app in the mobile web app section in Facebook for the same myfbapp. I did that and as expected when I login to facebook from my android phone myfbapp is listed under the apps section, so far so good. The problem starts when I click on the app. I get the request on my app server but it doesn't contain the signed_request , user_id etc.. ????? I was expecting the mobile app to work the same way as the canvas app but apparently it doesn't or I'm doing some thing wrong.
Then I started reading more about facebook mobile app at http://developers.facebook.com/docs/guides/mobile/web/#register where it talks about adding various Facebook Javascript API's in the index.html (I never did anything like that in my canvas app) and then I started thinking , may be then mobile web app is more (or exactly) like a regular web app with FB connect and not like canvas application (meaning it doesn't really load with in Facebook) , is this true?
On mobile facebook you can not see any custom pages/tabs. They are apparently wokring on that at the moment.
So it will be different to a canvas app. Your mobile app will be a completely seperate site and page not in an iFrame on Facebook.