Q:

iPhone and Facebook access tokens expiration date

So I know Facebook access tokens have an expiration date. What does this mean though?
Does this mean every time I need to post something on their FB wall, and it expires, it will need to ask them to login again to Facebook? Assume I requested permissions already..

A:

expires_in part of access token part means how many seconds from the time the oauth response was generated till the access token expires. For example, the value "3600" denotes that the access token will expire in one hour from the time the response was generated.  
If for example you post something to the user's wall using graph API, you'll get oauth exception that user's access token is expired. In that case depending on your implementation you can "refresh" the access token without a need to reauthorize or reauthorize the user. You can also request offline_access extended permission from the user. In that case access token generated will not expire. In iOS many implementations use offline_access.

