Using a filter in an iOS / Objective-C application to automatically log a user back into the Mobile Service if any request returns a 401 (for example, due to a timeout of the token).

TodoService.m

// This is the MSFilter protocol implementation taken from the iOS Mobile Services'\
// quickstart and modified to log the user in if a 401 Unauthorized response is received

#pragma mark * MSFilter methods

- (void) handleRequest:(NSURLRequest *)request
                onNext:(MSFilterNextBlock)onNext
            onResponse:(MSFilterResponseBlock)onResponse
{    
    // Increment the busy counter before sending the request
    [self busy:YES];
    onNext(request, ^(NSHTTPURLResponse *response, NSData *data, NSError *error){
        [self filterResponse:response
                     forData:data
                   withError:error
                  forRequest:request
                      onNext:onNext
                  onResponse:onResponse];
    });
}

- (void) filterResponse: (NSHTTPURLResponse *) response
         forData: (NSData *) data
       withError: (NSError *) error
      forRequest:(NSURLRequest *) request
          onNext:(MSFilterNextBlock) onNext
      onResponse: (MSFilterResponseBlock) onResponse
{    
    if (response.statusCode == 401) {
        // do login
        [self.client loginWithProvider:@"twitter" onController:[[[[UIApplication sharedApplication] delegate] window] rootViewController] animated:YES completion:^(MSUser *user, NSError *error) {
            if (error && error.code == -9001) {
                // user cancelled authentication - return the original response
                [self busy:NO];
                onResponse(response, data, error);
                return;
            }
            NSMutableURLRequest *newRequest = [request mutableCopy];
            [newRequest setValue:self.client.currentUser.mobileServiceAuthenticationToken forHTTPHeaderField:@"X-ZUMO-AUTH"];
            onNext(newRequest, ^(NSHTTPURLResponse *innerResponse, NSData *innerData, NSError *innerError){
                [self filterResponse:innerResponse
                             forData:innerData
                           withError:innerError
                          forRequest:request
                              onNext:onNext
                          onResponse:onResponse];
            });
        }];
    }
    else {
        [self busy:NO];
        onResponse(response, data, error);
    }
}

I'd love suggestions on how to make this code more elegant!