Objective-C Twitter three-legged authorization flow

BITwitterAuthenticator.h

//
//  BITwitterAuthenticator.h
//
//  Created by Bryan Irace on 8/9/12.
//  http://bryan.mit-license.org
//

@interface BITwitterAuthenticator : NSObject

@property (nonatomic, copy) NSString *OAuthConsumerToken;
@property (nonatomic, copy) NSString *OAuthConsumerSecret;

// 1) Callback parameter: authorization URL (load in an in-app browser or Mobile Safari)
- (void)authorizationURL:(void(^)(NSString *))callback;

// 2) Twitter will hit your application's callback URL (parameters: request token, verifier)

// 3) Callback parameters: OAuth token, secret
- (void)accessToken:(NSString *)requestToken verifier:(NSString *)verifier 
           callback:(void(^)(NSString *, NSString *))callback;

@end

BITwitterAuthenticator.m

//
//  BITwitterAuthenticator.m
//
//  Created by Bryan Irace on 8/9/12.
//  http://bryan.mit-license.org
//

#import "BITwitterAuthenticator.h"

@implementation BITwitterAuthenticator {
    HTTPRequestQueue *_requestQueue;
}

- (void)authorizationURL:(void(^)(NSString *))callback {
    __block HTTPRequest *request = [_requestQueue postRequestWithPath:@"oauth/request_token"];
    
    request.completionBlock = ^ {        
        if (callback) {
            NSDictionary *response = request.responseJSON;

            dispatch_async(dispatch_get_main_queue(), ^{
                callback([NSString stringWithFormat:@"https://api.twitter.com/oauth/authorize?oauth_token=%@", 
                          response[@"oauth_token"]]);
            });
        }
    };
    
    [_requestQueue addOperation:request];
}

- (void)accessToken:(NSString *)requestToken verifier:(NSString *)verifier 
           callback:(void(^)(NSString *, NSString *))callback {
    __block HTTPRequest *request = [_requestQueue postRequestWithPath:@"oauth/access_token"];
    request.OAuthToken = requestToken;
    [request addParameter:verifier forKey:@"oauth_verifier"];
    
    request.completionBlock = ^ {
        if (callback) {
            NSDictionary *response =request.responseJSON;

            dispatch_async(dispatch_get_main_queue(), ^{
                callback(response[@"oauth_token"], response[@"oauth_token_secret"]);
            });
        }
    };
    
    [_requestQueue addOperation:request];
}

#pragma mark - NSObject

- (id)init {
    if (self = [super init]) {
        _requestQueue = [[HTTPRequestQueue alloc] init];
        _requestQueue.baseURL = @"https://api.twitter.com";
        _requestQueue.maxConcurrentOperationCount = 1;
        _requestQueue.OAuthConsumerKey = self.OAuthConsumerKey;
        _requestQueue.OAuthConsumerSecret = self.OAuthConsumerSecret
    }
    
    return self;
}

- (void)dealloc {
    [_requestQueue release];
    
    [super dealloc];
}

@end