Ensuring non-expired token before every request
You could introduce a delegate instead passing another block in loadCategories method. 

First, the protocol:

@protocol ASMyApiCategoriesDelegate &lt;NSObject&gt;

    @required
    - (void) ASMyApiCategoriesDidLoad:(NSArray *)categories;
    - (void) ASMyApiCategoriesDidFailToLoadWithError:(NSError *)error

@end


You change the signature of + [ASMyApi loadCategories:completionBlock:] to accept a delegate:

+ (void) loadCategoriesToken:(id)token delegate:(id &lt;ASMyApiCategoriesDelegate&gt;)delegate
{
    NSArray *categories;
    // code that loads categories

    if (categories)
    {
        [delegate ASMyApiCategoriesDidLoad:categories];
    }
    else
    {
        [delegate ASMyApiCategoriesDidFailToLoadWithError:nil];
    }
}


In your view controller you'll have to implement the required methods from ASMyApiCategoriesDelegate protocol and update loadCategories method.

- (void) ASMyApiCategoriesDelegateDidLoad:(NSArray *)categories
{
    [self.refreshControl endRefreshing];
    self.categories = categories;
    [self updateUI];
}

- (void) ASMyApiCategoriesDelegateDidFailToLoadWithError:(NSError *)error
{
    [self.refreshControl endRefreshing];
    [self monitorNetworkReachability];
}

- (IBAction) loadCategories
{
    [self.refreshControl beginRefreshing];
    [((AppDelegate *)[UIApplication sharedApplication].delegate) fetchTokenWithCompletionBlock:^(ASToken *token, NSError *error) {
        if (token)
        {
            [ASMyApi loadCategories:token.token delegate:self];
        }
        else
        {
            [self ASMyApiCategoriesDidFailToLoadWithError:nil];
        }
    }];
}