How to handle Facebook's deprecation of offline_access when you use token both in both iOS app and a server

Question

Facebook\'s deprecation of the offline_access permission is coming May 2012 and the documentation isn\'t giving us enough information on how to handle it.

W

Answer 1

Great answer, one important addition : the default token lasts between 1 and 2 hours. You get the remaining of the hour during which the user signs up, plus 1 full hour. For example if a user signs up at 3:45pm, the access token will expire at 5pm. To be safe developers should assume it only lasts 1hour.

Answer 2

Overview

I believe that the root of what facebook is trying to achieve is to prevent an app from having perpetual ever-lasting access to a user's account. So, with the new migration an app can only access an account for 60 days unless the user signs in again.

I don't work for facebook, but here are my findings from playing around with the facebook graph api.

General Solution

1. Whenever a user signs in, take their access token and immediately extend/refresh it, and save it
2. Record the expiration date of the access token
3. When an access token expires (either from the recorded date, or a graph API exception telling you so), then notify the user that you don't have access, and ask them to sign in again.

Answers

A. When you authenticate through the newest Facebook iOS SDK, what is the default lifetime of the access token you get? This document says an extended token request will give you one that lasts 60 days. This other document talks about the first access token request and mentions varying validities but it's unclear and does it talk about specific validity times:

Here's how it works:

1. The first sign-in grants you approximately two hours
2. By refreshing the access token, you can get up to 60 days
3. If the user doesn't sign in to those 60 days, there is no way to get access for longer without having them sign in.
4. If the user de-authorizes your app, that 60 day windows ends immediately, and you will no longer have access.

B. For the client, now that the access token isn't necessarily long lived, is the right approach for us to: Let use login through FB, then detect whenever the access token is expired. If it is, then call into FB iOS SDK to re-authentication/re-authorize? (this should just trigger user to bounce out to FB iOS app, and in most cases come immediately back to our app with a new access token).

If the users access token is expired, your only option is to have them go through a login loop like you are talking about.

C. According to this blog post I found, you can only extend an access token once. On the client, I can just handle this by prompting a re-authentication/re-authorization as I mentioned in Question B. However, this doesn't work on our server. We could certainly have the server renew it once to 60 days, but what happens on the 61st day? The server just stops being able to sync the friend's list?

You can only extend an access token once. On the 61st day, you are out of luck. Best notify the user and let them know that unless they sign in, you won't be able to do anything.

D. It seems to make sense to check the validity of the FB access token every time the app starts or re-hydrates from sleep. What is the best way for our iOS app to check this? Is there a recommended endpoint to call to validate a token? Should we just call into https://graph.facebook.com/me passing the access token and checking the response?

I haven't be able to find an API equivalent of the Debug Console. This FB blog article talks about invalidated access tokens, but doesn't mention any API methods in particular meant to test the API.

I your suggestion of hitting https://graph.facebook.com/me would work just fine is exactly what they recommend in their example. In fact, I might use this approach in my app as a pro-active way of checking an access token.

Tid Bits

• When you "refresh" an access token, a new access token will be returned. The response looks like: access_token=TOKEN&expires=5183912
• You can only "refresh" an access token once. If you try to "refresh" the long-lived token returned from a previous call, it will return the same token, but doesn't throw an exception unless the token has expired. (in other words, you can safely try to refresh your token)
• The default access token length seems to be around 2 hours
• If you "refresh" an access token, that new access tokens seems to be the one that you'll get from the facebook API afterwards (instead of returning the original, short-lived access token)

Also, if you want to play around, these tools make it easy to test out your use case in a browser before burying it in your code:

• Graph API Explorer - For creating and getting access tokens
• Debug Console - For checking the expiry date of tokens before/after refresh
• Refresh Endpoint - For manually testing extending your tokens