Facebook Page application tab: when do I get a signed_request and when do I get a fb_sig_page_id?

I don't know how to ask this question properly. I think the title is not clear at all, anyway here's the problem.

I'm developing an application for Facebook pages, which adds a tab to the page. I noticed that I sometimes get a signed_request string, which, properly parsed, 开发者_JAVA百科allows me to extract a page id, but some other time I get a bunch of POST data, and not a signed request... and among this data there are many variables like fb_sig_page_id and other ones.

I don't understand why I am sometime getting signed_request and some other times the POST data. Can anyone help me out?

This question I asked on the FB developer forums adds a bit more detail: http://forum.developers.facebook.net/viewtopic.php?pid=316812#p316812

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It depends on how your Facebook Application is configured. In the "Advanced" section of the Facebook configuration of your App, it is the "OAuth 2.0 for Canvas" setting. If this is set to true, then you will get the signed_request. If it is set to false, then you get the fb_sig_page_id.

The default changed at some point, so your older apps will have this setting set to false, and your newer apps will have it set to true.