gistfile1.m

ACAccountStore *as = [[ACAccountStore alloc] init];
[self setAccountStore:as]; 
ACAccountType *twitterAccountType = [[self accountStore] accountTypeWithAccountTypeIdentifier:ACAccountTypeIdentifierTwitter];

[[self accountStore] requestAccessToAccountsWithType:twitterAccountType
                 withCompletionHandler:^(BOOL granted, NSError *error) {
                   if ( granted == NO ) {
                     [self showNoTwitterAccountAlert]; 
                     return;
                   }
                   
                   NSArray *twitterAccounts = [[self accountStore] accountsWithAccountType:twitterAccountType];
                   if ( [twitterAccounts count] > 0 ) {
                     [self setTwitterAccount:[twitterAccounts lastObject]];
                     [self retrieveIDs];
                   } else {
                     [self showNoTwitterAccountAlert];
                   }
                 }];