Is it possible to pass parameters to the callback URL of a FB app which is accessed through a tab?

Question

I have this facebook application which adds a custom tab to fan pages. You access the tab by an URL like:

http://www.facebook.com/pages/PAGE-NAME-HERE/PAGE-ID?v=APP-ID

I want to be able to add some extra get parameters to that URL, but it seems they don't get passed correctly because facebook is filtering them. Is there a way to pass those parameters? Even not via GET but some other kind of technique.

Answer 1

If you want to pass multiple querystring params though the app_data param, you can urlencode it.

All querystring params that need to propagate through a Facebook tab should be url-encoded in the app_data var.

In other words, the "&" and the "=" need to be url-encoded (especially if passing more than one param).

Examples

GOOD TAB URL (this passes all 3 params):

https://www.facebook.com/pages/yourpagename/56789?sk=app_12345&app_data=var1%3D123456789%26anothervar%3Drawr%26athird%3Dmeow

In the app_data from this signed request, I got this value: var1=123456789&anothervar=rawr&athird=meow

BAD TAB URL (this passes only the first param through the signed_request):

https://www.facebook.com/pages/yourpagename/12345?sk=app_56789&app_data=var1=123456789&anothervar=rawr&athird=meow

In the app_data from this signed request, I ONLY got this value: var1=123456789 (Facebook dropped the rest)

You can even give your media team instructions like this =)

Media team,

Here is an online utility to urlencode the querysting data you want to embed in the app_data param: http://meyerweb.com/eric/tools/dencoder/

Base Url: https://www.facebook.com/pages/yourpagename/12345?sk=app_56789&app_data=

Steps:

1. Go to http://meyerweb.com/eric/tools/dencoder/
2. Type var1=123456789&anothervar=rawr&athird=meow in the box
3. Hit the Encode button
4. You’ll get var1%3D123456789%26anothervar%3Drawr%26athird%3Dmeow which becomes your app_data param. Append that to the baseUrl noted above like this: https://www.facebook.com/pages/yourpagename/12345?sk=app_56789&app_data=var1%3D123456789%26anothervar%3Drawr%26athird%3Dmeow (this is the URL with the tracking params for the [banner ad] [online media] [etc])

p.s. Querystring params in non-tab pages are handled fine (https://apps.facebook.com/yourappname/Canvas.aspx?var1=123456789&anothervar=rawr&athird=meow does not strip out qs params like what happens in the Tab, for example).