Getting an Authentication Failed error from server after hitting web service in Swift

Question

The following below code is of hitting web service in swift by using NSURLSession .. I always get authentication failed message from server.Not able to get what is missing in request body.

  let urlString:String = "\(BaseURL)"+"user_register.php?"  
    let deviceStr = "xyz"

    let dictParam:NSDictionary = ["email":"\((emailTF?.text!)!)","username":"\((usernameTF?.text!)!)","password":"\((passwordTF?.text!)!)","device_key":deviceStr]


    print(dictParam)

    let session = NSURLSession.sharedSession()

    let request = NSMutableURLRequest(URL: NSURL(string: urlString)!)

    request.cachePolicy = NSURLRequestCachePolicy.ReloadIgnoringCacheData
    request.timeoutInterval = 60.0

    request.addValue("application/json", forHTTPHeaderField: "Content-Type")

  //  request.addValue("application/json", forHTTPHeaderField: "Accept")


    request.HTTPMethod = "POST"

    let dataToPost = try! NSJSONSerialization.dataWithJSONObject(dictParam, options: [])

    request.HTTPBody = dataToPost

    let task = session.dataTaskWithRequest(request) {
        (
        let data, let response, let error) in

        guard let _:NSData = data, let _:NSURLResponse = response  where error == nil else {
            print("error")
            return
        }


        let response:AnyObject! = try! NSJSONSerialization.JSONObjectWithData(data!, options: [])

        print(data!)


        print(response)

    }

    task.resume()