Fb SSO for iPhone application

I am building an iPhone app that uses Facebook login.

I recently changed it to SSO but its asking users to sign again after 8 hours. Is there a way to improve on timeout for Facebook SSO ?开发者_运维问答

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Request permission for offline access.

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Just an update, offline_access is being deprecated, you can now implement a 'sliding expiry' using the latest SDK - so the more a user uses your app, the less often they will need to log in. See http://developers.facebook.com/docs/mobile/ios/build/#extend_token