I had this implemented for a customer who is still on OpenAM 11 and integrating with Facebook via Graph API version 2.0. Facebook Graph API is already v2.8
Recently we re-configured OpenAM to update the Facebook Graph API to v2.8. I realized we can no longer retrieved long-lived access token from Facebook.
The codes used to look like:
// Need to strip:// e.g. access_token=[LONG-LIVED-ACCESS-TOKEN]&expires=5148647
longLivedToken = longLivedToken.substring(13,longLivedToken.indexOf("&"));
It was returned as a String.
In Facebook Graph API to v2.8, the response format has been changed to JSON.