title: How to add custom header to AFNetworking on a JSONRequestOperation
body: <p>Hi, I have the following code accessing a URL:</p>
  
  <pre><code>NSString * stringURL = [NSString stringWithFormat:@"%@/%@/someAPI", kSERVICE_URL, kSERVICE_VERSION];
  NSURLRequest * request = [NSURLRequest requestWithURL:[NSURL URLWithString:stringURL]];
  
  AFJSONRequestOperation * operation = [AFJSONRequestOperation JSONRequestOperationWithRequest:request success:^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON) {
      completionHandler(JSON, nil);
  } failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error, id JSON) {
      completionHandler(nil, error);
  }];
  </code></pre>
  
  <p>But I want to pass the user token as a parameter on <code>HEADER</code>, like <code>X-USER-TOKEN</code>.</p>
  
  <p>Cant find it on <code>AFNetworking documentation</code>, should I change the operation type?</p>