converting a curl request to groovy / grails HTTPBuilder request

I am doing a curl request :-

curl -X POST -H "Content-Type: application/json" -H "Accept: application/json,text/javascript" -d '[{"command": "system.login", "password": "guesswhatIam", "user": "theuser"}]' -k "https://TheIpAddress/ajax?sid="

The response I am getting from curl is :-

[{"status":"ok","sid":"7dfb39fd-2945-46d8-9036-81bb4ff2d858","deadtime":0}]

I'm trying to work out how to do the equivalent in Grails using HTTPBuilder, and I'd very much like to pull out that sid value.

I have tried this :-

    def http = new HTTPBuilder ('https://' + ipAddress+'/ajax?sid=')
    http.ignoreSSLIssues()
    http.headers = [Accept: 'application/json,text/javascript', charset: 'UTF-8', ContentType: 'application/json' ]
    http.request(POST) {
        uri.path = ''
        body = ['[{"command": "system.login", "password": "thepassword", "user": "theuser"}]']
        requestContentType = ContentType.JSON
        response.success = { resp,json ->
            print "Success! ${resp.status}"
            print json
        }

        response.failure = { resp ->
            println "Request failed with status ${resp.status}"
        }
    }

I get a 200 success, but I cant seem to parse the data I get beck - I seem to get null?

Any pointers would be gratefully received.

So, in the end I gaveup with HTTPBuilder, and reverted to Java. This did the trick for me :-

    import java.io.IOException;
    import java.io.InputStream;
    import java.io.OutputStreamWriter;
    import java.net.HttpURLConnection;
    import java.net.URL;
    import java.util.Scanner;

    URL url = new URL("http://" + ipAddress + "/ajax?sid=");
    HttpURLConnection httpConn = (HttpURLConnection) url.openConnection();
    httpConn.setRequestMethod("POST");
    httpConn.setRequestProperty("Content-Type", "application/json");
    httpConn.setRequestProperty("Accept", "application/json,text/javascript");
    httpConn.setDoOutput(true);
    OutputStreamWriter writer = new OutputStreamWriter(httpConn.getOutputStream());        
    writer.write("[{\"command\": \"system.login\", \"password\": \"thePassworrd\", \"user\": \"theUser\"}]");
    writer.flush();
    writer.close();
    httpConn.getOutputStream().close();
    InputStream responseStream = httpConn.getResponseCode() / 100 == 2
            ? httpConn.getInputStream()
            : httpConn.getErrorStream();
    Scanner s = new Scanner(responseStream).useDelimiter("\\A");
    String response = s.hasNext() ? s.next() : "";
    return response;

I hope this helps someone else with a similar problem.