Calling Wcf .svc webservice in XCode

Question

I have a WCF .svc webservice which takes two parameters username and passwrod and returns a Json object. Can anyone tell me in details how to call the webservice and parse it in Xcode. I am trying to use this webservice in my Login screen. The webservice link is https://xxxx.xxxx.com/IOsServices/Service1.svc.