Native Facebook Login stopped working after SDK update to 3.14

I just ran to this issue also, here's the details on what has happened & how I fixed my app.

Bottom line
Due to the new login process wherein users can now approve / deny each requested permission (something not supported by the native ios integrated login), Facebook has changed the sdk's default login behavior to first try the Facebook fast app switch & then fall back on the web view, completely ignoring any ios system level Facebook credentials.

This is noted in the upgrade guide (form 3.13 > 3.14) here: https://developers.facebook.com/docs/ios/upgrading

Relevant portion:
"The default login behavior has changed from FBSessionLoginBehaviorUseSystemAccountIfPresent to FBSessionLoginBehaviorWithFallbackToWebView."

So what to do?
Well, if you don't need any of the new things, FBLikeControl etc..., that were introduced in 3.14, you could just downgrade to 3.13. However, if you want/need to use 3.14n there's an instance method on FBSession that takes the FBSessionLoginBehavior as a parameter: https://developers.facebook.com/docs/reference/ios/current/class/FBSession/#openWithBehavior:completionHandler:

I updated the body of my method for opening a Facebook session from:

    [FBSession openActiveSessionWithReadPermissions:@[@"email", @"user_location"]                                       allowLoginUI:YES                                  completionHandler:                                          ^(FBSession *session, FBSessionState state, NSError *error) {                                              [self sessionStateChanged:session state:state error:error];                                          }    ];

to:

    FBSessionStateHandler completionHandler = ^(FBSession *session, FBSessionState status, NSError *error) {        [self sessionStateChanged:session state:status error:error];    };    if ([FBSession activeSession].state == FBSessionStateCreatedTokenLoaded) {        // we have a cached token, so open the session        [[FBSession activeSession] openWithBehavior:FBSessionLoginBehaviorUseSystemAccountIfPresent                  completionHandler:completionHandler];    } else {        [self clearAllUserInfo];        // create a new facebook session        FBSession *fbSession = [[FBSession alloc] initWithPermissions:@[@"email", @"user_location"]];        [FBSession setActiveSession:fbSession];        [fbSession openWithBehavior:FBSessionLoginBehaviorUseSystemAccountIfPresent                  completionHandler:completionHandler];    }

NOTE: my clearAllUserInfo method includes the following lines:

    [FBSession.activeSession closeAndClearTokenInformation];    [FBSession renewSystemCredentials:^(ACAccountCredentialRenewResult result, NSError *error) {        NSLog(@"%@", error);    }];    [FBSession setActiveSession:nil];

It's also worth checking out the Facebook documentation on understanding sessions: http://developers.facebook.com/docs/facebook-login/ios/v2.0#sessions

Check the permissions you ask for, in the new SDK (3.14) the basic_info permission has been deprecated and you need to submit the app for review for extended permissions. The basic permissions are: public_profile, email, and user_friends

More info here: https://developers.facebook.com/docs/ios/upgrading

Perhaps you may be missing this method:

- (BOOL)application:(UIApplication *)application handleOpenURL:(NSURL *)url{    return [FBSession.activeSession handleOpenURL:url];}

It helped my case in which I had to migrate from 3.9.0 to the latest. Hope it helps.