- Extending existing offline access_tokens
- https://graph.facebook.com/oauth/access_token?
- client_id=APP_ID&
- client_secret=APP_SECRET&
- grant_type=fb_exchange_token&
- fb_exchange_token=EXISTING_ACCESS_TOKEN
- access_token=xxxxxxx&expires=5102358
- $request_url = "https://graph.facebook.com/oauth/access_token?client_id=xxxx&client_secret=xxxx&grant_type=fb_exchange_token&fb_exchange_token=xxxx";