Facebook SDK 3.1 - Error validating access token

Question

I'm trying to transition my app to the new Facebook SDK 3.1 (with support for iOS6 authentication).

I had it working just fine, so I then decided to remove the app from my list of authorized apps on the FB website in order to test that iOS would ask for permission again.

Now my first call to [FBRequest requestForMe] causes this error:

Response:

{
  "error": {
    "message": "Error validating access token: Session does not match current stored session. This may be because the user changed the password since the time the session was created or Facebook has changed the session for security reasons.",
    "type":"OAuthException",
    "code":190,
    "error_subcode":460
  }
}

Some details:

I'm trying to open the session as follows :

   [FBSession openActiveSessionWithReadPermissions:nil
                                       allowLoginUI:YES
                                  completionHandler:^(FBSession *session, FBSessionState state, NSError *error) {

                                           switch (state) {
                                               case FBSessionStateOpen:
                                                   [self presentPostOptions];
                                                   break;

                                               case FBSessionStateClosed:
                                               case FBSessionStateClosedLoginFailed:
                                                   [FBSession.activeSession closeAndClearTokenInformation];
                                                   break;

                                               default:
                                                   break;
                                           }

I then get called back in state FBSessionStateOpen (at this point iOS hasn't presented a request dialog, is that to be expected)? Facebook logs this:

2012-09-26 13:43:43.768 MyApp[2177:907] FBSDKLog: FBSession INVALID transition from FBSessionStateCreated to FBSessionStateClosed
2012-09-26 13:43:43.769 MyApp[2177:907] FBSDKLog: FBSession transition from FBSessionStateCreated to FBSessionStateCreatedOpening 
2012-09-26 13:43:43.837 MyApp[2177:907] FBSDKLog: FBSession transition from FBSessionStateCreatedOpening to FBSessionStateOpen 

Once the session is open, in presentPostOptions I do this:

- (void)presentPostOptions
{    
    [[FBRequest requestForMe] startWithCompletionHandler:^(FBRequestConnection *connection, NSDictionary<FBGraphUser> *user, NSError *error) {
        if (!error) {
            self.usersName = user.name;
            self.usersID = user.id;

            [self getPages];
        }
        else
        {
            [self didFailWithError:error];
        }
    }];
}

Before the above completion block is called back, my main state handler block is called with an FBSessionStateClosed state. In the meantime, the Facebook SDK has logged the above error.

I can't find any way to reset the system; nor do I really understand the cause.

Can anyone please shed some light?

Answer 1

The Facebook account on the device has become out-of-sync with the server as well as with the App's/SDK's cache. This can be solved by calling the ACAccountStore method renewCredentialsForAccount, which will update the OS's understanding of the token state.

In the next update of the SDK, the SDK will automatically call this API when it receives a response from the server indicating that a token has become invalid. For the 3.1.0 revision of the SDK, applications will need to explicitly call this API. Here is a code sample:

ACAccountStore *accountStore;
ACAccountType *accountTypeFB;
if ((accountStore = [[ACAccountStore alloc] init]) &&
    (accountTypeFB = [accountStore accountTypeWithAccountTypeIdentifier:ACAccountTypeIdentifierFacebook] ) ){

    NSArray *fbAccounts = [accountStore accountsWithAccountType:accountTypeFB];
    id account;
    if (fbAccounts && [fbAccounts count] > 0 &&
        (account = [fbAccounts objectAtIndex:0])){

        [accountStore renewCredentialsForAccount:account completion:^(ACAccountCredentialRenewResult renewResult, NSError *error) {
            //we don't actually need to inspect renewResult or error.
            if (error){

            }
        }];
    }
}

There are several options for where/when to call the API. The simplest place would be to opportunistically make the call on application launch, or on view load. One problem with this approach is that it will cause a network round-trip that is often unnecessary. Another option is to call it when a session change notification occurs, indicating that a session has closed. Also many applications fetch some basic information such as graph.facebook.com/me, at application launch time, and if so -- a call to this method in case of an error response may be a reasonable place to ask iOS to update its token status.

Hopefully this helps!