iOS AC + Social(Facebook) Framework & Rails(omniauth-facebook)

Gemfile

gem 'devise'
gem 'omniauth-facebook'

omniauth_callbacks_controller.rb

class Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController
  skip_before_filter :verify_authenticity_token

  def facebook
    @user = User.from_omniauth(request.env["omniauth.auth"])

    if @user.persisted?
      sign_in_and_redirect @user, :event => :authentication
      set_flash_message(:notice, :success, :kind => "Facebook") if is_navigational_format?
    else
      session["devise.facebook_data"] = request.env["omniauth.auth"]
      redirect_to new_user_registration_url
    end
  end
end

routes.rb

Rails.application.routes.draw do
  devise_for :users, :controllers => { :omniauth_callbacks => "users/omniauth_callbacks" }
end

ViewController.h

#import <UIKit/UIKit.h>
#import <Accounts/Accounts.h>
#import <Social/Social.h>
@interface ViewController : UIViewController

@property (nonatomic, strong) ACAccountStore *accountStore;
@property (nonatomic, strong) ACAccountCredential *accountCredential;

@end

ViewController.m

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
- (IBAction)signInFacebook:(id)sender {
    
    self.accountStore = [[ACAccountStore alloc] init];
    ACAccountType *fbAccountType = [self.accountStore accountTypeWithAccountTypeIdentifier:ACAccountTypeIdentifierFacebook];
    
    id options = @{
                   ACFacebookAppIdKey: @"myAPikeyhere",
                   ACFacebookPermissionsKey: @[@"email", @"read_friendlists"],
                   ACFacebookAudienceKey: ACFacebookAudienceFriends
                   };
    
    [self.accountStore requestAccessToAccountsWithType:fbAccountType
                                               options:options
                                            completion:^(BOOL granted, NSError *error) {
                                                if (granted) {
                                                    ACAccount *fbAccount = [[self.accountStore accountsWithAccountType:fbAccountType] lastObject];
                                                    ACAccountCredential *facebookCredential = [fbAccount credential];
                                                    NSString *token = [facebookCredential oauthToken];
                                                    [self authenticate:token];
                                                } else{
                                                    NSLog(@"Not granted: %@", error);
                                                }
                                            }];
    
   
}

- (void)authenticate:(NSString *)token {
    NSURL *url = [NSURL URLWithString:@"http://localhost:3000/users/auth/facebook/callback"];
    
    NSMutableURLRequest *req = [[NSMutableURLRequest alloc] initWithURL:url];
    
    NSString *params = [NSString stringWithFormat:@"access_token=%@", token];
    [req setHTTPMethod:@"POST"];
    [req setHTTPBody:[params dataUsingEncoding:NSUTF8StringEncoding]];
    
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        NSURLResponse *res;
        NSError *err;
        [NSURLConnection sendSynchronousRequest:req returningResponse:&res error:&err];
        if (!err) {
            NSLog(@"The user is logged in on the server side too");
        } else {
            NSLog(@"Error occurred. %@", err);
        }
    });
}

@end