How to send JSON request to service with parameters in Objective-C

I'm creating a iPhone app, and im trying to figure out how to create a JSON request to the webserice that contains parameters. In Java this would look like this

HashMap<String, String> headers = new HashMap<String, String>();
 
 JSONObject json = new JSONObject();
 
             json.put("nid", null);
             json.put("vocab", null);
             json.put("inturl", testoverview);
             json.put("mail", username); // something@gmail.com
             json.put("md5pw", password); // donkeykong
 
         headers.put("X-FBR-App", json.toString());
 

The header has to contain a JSON object and "X-FBR-App" before the service recognizes the request. How would this be implemented in Objective-C ?

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