How do I get the session_key for a permanent "offline_access" permission?

I writing a server-side backend for a mobile app that will allow posting media to facebook. I need to post images to the user's profile.

I get the user to add the application + the user allows me to offline_access

From Facebook documentation I see that I need to pass the "session_key" on every api request I am doing (using the restful API).

I've forwarded the user to prompt开发者_开发百科_permissions.php but when he allows the offline_access - I don't get any signature/key.

What am I doing wrong?

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look for the cookie labeled:

$APIKEY_session_key

where $APIKEY is your API key.

this cookie contains the offline session key that you can use.