how to detect Action Back Button and False Block ???

[ishrek]

` [authenticationContext acquireTokenWithResource:kOffice_365_API_Discovery clientId:clientId redirectUri:redirectUri completionBlock:^(ADAuthenticationResult *result) {

        [[UIApplication sharedApplication] beginIgnoringInteractionEvents];

        switch (result.status) {
            case AD_SUCCEEDED:
               break;
            case AD_USER_CANCELLED:
                break;
            case AD_FAILED:
                // Authentication failed -
                break;
        }
    }];`

I debug in this code discovered one problem is : when login fasle and action Back Button (in View Login One Drive) are running in the AD_FAILED case. how to detect the action back button ???. Please help me