Now we are discussing how to handle expire user access token. Normally we are getting expired session or does not authenticate access token exception when we are communicating with Facebook client api.
To handle this type error Facebook provide exchange access token function.
In api we just pass old user access token and get new access token.
Code

https://graph.facebook.com/oauth/access_token?client_id=$appid&client_secret=$app_secret&grant_type=fb_exchange_token&fb_exchange_token=$expiredToken

Facebook tools:

Facebook tool to get list of pages/apps with user token:
access Token

Facebook tool to to check token details:
Token Debugger